Determining a Flow Characteristic of a Material in a Structure

ABSTRACT

An volume of a patient can be mapped with a system operable to identify a plurality of locations and save a plurality of locations of a mapping instrument. The mapping instrument can include one or more electrodes that can sense a voltage that can be correlated to a three dimensional location of the electrode at the time of the sensing or measurement. Therefore, a map of a volume can be determined based upon the sensing of the plurality of points without the use of other imaging devices. An implantable medical device can then be navigated relative to the mapping data.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/421,364, filed Apr. 9, 2009, entitled “Method and Apparatus forMapping a Structure,” which is a continuation-in-part of U.S.application Ser. No. 12/117,537, filed May 8, 2008, entitled “Method andApparatus for Mapping a Structure,” which claims benefit of U.S.Provisional Application No. 61/046,298, filed Apr. 18, 2008, entitled“Method and Apparatus for Mapping A Structure.” The disclosures of allof the above identified applications are incorporated herein byreference.

This application also includes subject matter related to the subjectmatter disclosed in U.S. patent application Ser. No. 12/421,375, filedon Apr. 9, 2009; and U.S. patent application Ser. No. 12/421,332, filedon Apr. 9, 2009; and U.S. application Ser. No. 12/117,549, filed May 8,2008, entitled “Method and Apparatus for Mapping a Structure.” Thedisclosures of all of the above identified applications are incorporatedherein by reference.

FIELD

The present disclosure relates generally to anatomical positiondetermination, and particularly to mapping an anatomical region andillustrating the map.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

The human anatomy includes many types of tissue that can eithervoluntarily or involuntarily, perform certain functions. After diseaseor injury, or due to certain genetic predispositions certain tissues mayno longer operate within general anatomical norms. For example, afterdisease, injury, time, or combinations thereof, the heart muscle maybegin to experience certain failures or deficiencies. These failures ordeficiencies may be corrected or treated with implantable medicaldevices (IMDs), such as implantable pacemakers, implantable cardioverterdefibrillator (ICD) devices, cardiac resynchronization therapydefibrillator devices, or combinations thereof.

One of the main portions of the IMD can include one or more leads thatare directly connected to tissue to be affected or treated by the IMD.The lead can include a tip or electrode portion that is directlyconnected to a first portion of the anatomical tissue, such as a musclebundle, and a lead body that connects to the second main portion, whichis the device body or therapeutic driving device. It is generally knownthat the device body or case portion can be implanted in a selectedportion of the anatomical structure, such as in a chest or abdomen, andthe lead can be inserted through various venous portions so that the tipportion can be positioned at the selected position near or in the heartmuscle.

The IMDs are implantable devices that may require the use of imagingdevices for implantation. The imaging devices can include fluoroscopesthat expose a patient and a surgeon to ionizing radiation. In addition,the use of the imaging device can require time for acquiring image dataand understanding the images from the image data. For example,considerable experience and training may be required for properinterpretation of fluoroscopic images.

The use of various imaging devices can require various additional costsand procedures. For example, fluoroscope devices employ ionizingradiation to acquire images of a patient. Individuals, such as surgeonsand technicians that attend the implantation procedure may be constantlyor repeatedly exposed to the ionizing radiation and are generallyrequired to wear protective clothing. The protective clothing, however,can be heavy and may strain operators and staff. In addition, theimaging devices, such as fluoroscopes, magnetic resonance imagers,ultrasound systems, can be relatively expensive and require extensivetraining in the use of the imaging device. Due to cost and trainingrequirements, therefore, certain facilities may forego acquiring theimaging devices thereby reducing the number of facilities able toperform certain procedures.

SUMMARY

A position sensing unit (PSU) system is operable to map and illustratemapped and saved points. The system can determine the location orposition of a tracking or position element. The tracking element can bean electrode and a position is determined by generating a voltage in apatient and calculating an impedance at the electrode. The calculatedimpedance is used to determine the position of the electrode as in apatient or other appropriate conducting medium.

The saved points may be used to create a map determined with theelectrode that can be used to determine a location of a later positionedelectrode. The electrode positioned in the anatomy can include a pacinglead, defibrillation lead, or lead for any other purpose. The electrodecan generally be a part of an IMD. The map generated with the PSU can beused to guide or navigate a lead to a selected location without the useof other prior or concurrent imaging devices, such as an externalfluoroscope, magnetic resonance imaging (MRI), ultrasound (US), etc.

The use of the position sensing unit to generate a map can eliminate orreduce the need for another imaging device. The imaging devices, such asfluoroscopes, as discussed above, can require additional costs andtraining requirements that may be eliminated. For example, if afluoroscope is not used, protective clothing, such as a lead apron, maynot be required to be worn by individuals in a room and can reducestress and weight carried by the individuals. In addition, eliminationof ionizing radiation doses can benefit a patient and a user. Further,with the use of the position sensing unit and the elimination orreduction in use of another imaging device, a cost center or capitalinvestment may be reduced or eliminated while allowing a facility toperform selected procedures, as discussed herein.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is an environmental view of a mapping or navigation system;

FIG. 2 is a detailed view of a position sensing unit (PSU) andassociated devices, according to various embodiments;

FIG. 3 is a detailed view of a mapping catheter according to variousembodiments;

FIG. 4 is a detailed view of an implantable retractable lead with aretractable electrode, according to various embodiments;

FIG. 4A is a detailed view of the implantable retractable lead in aretracted configuration, according to various embodiments;

FIG. 4B is a detailed view of the implantable retractable lead in anextended configuration, according to various embodiments;

FIG. 5 is a view of a patient with a mapping catheter inserted into aninternal organ of the patient;

FIG. 5A is a detailed view of a mapping catheter inserted in a patient;

FIG. 6 is a detailed view of a display device with mapping dataillustrated thereon;

FIG. 7 is a flow chart illustrating a method of mapping with a positionsensing unit;

FIG. 8 is a detailed environmental view of a mapping catheter and adisplay device displaying related mapping information;

FIG. 9 is a flow chart illustrating a method of rendering a surfacebased on mapping information, according to various embodiments;

FIG. 10 is a display device illustrating raw mapping information andsurface rendered data;

FIG. 11 is a flow chart illustrating a method of rendering a surfacebased on mapping information, according to various embodiments;

FIG. 12 is a display device illustrating surface rendered data;

FIGS. 12A(i)-12C(ii) illustrates various embodiments of a lead withmultiple tracking electrodes and illustrations and a display thereof;

FIG. 13A is a detailed partial cut-away view of a heart and a leadpositioned therein with a guide wire;

FIG. 13B is an illustration on a display for tracking a lead with aguide wire;

FIG. 13C is a flowchart illustrating a method of tracking a guide wire;

FIG. 14 is a flowchart illustrating a method of displaying a threedimensional nature of data;

FIGS. 15A-15B illustrate an example of demonstrating a three dimensionalnature of data;

FIG. 16 is a view of an implantable medical device positioned within apatient;

FIG. 17 is a flowchart illustrating a method of correcting of adistortion;

FIGS. 18A and 18B illustrate a graphical representation of data beforeand after correcting for a distortion;

FIGS. 19A and 19B illustrate a graphical representation of data beforeand after correction for a distortion;

FIG. 20 is a flowchart illustrating a method of correcting a display fordistortions;

FIGS. 21A-21C is a schematic view of a mapping catheter and multiplevirtual points;

FIGS. 22A-22C is a graphical representation of a pathway generation anddisplay on a display device;

FIGS. 23A-23B is a graphical representation of displaying position data;

FIG. 24A is a schematic illustration of a heart with a lead positionedtherein;

FIG. 24B is a graphical representation of a surface based upon mappingdata;

FIG. 24C is a graphical illustration of data on a display device basedupon mapping data and sensor data;

FIG. 25 is a mapping catheter, according to various embodiments;

FIG. 26A is an illustration of a PSU and various physiological sensors;

FIG. 26B is a schematic view of a mapping catheter within a heart;

FIGS. 27A-27D illustrate schematic representations of an electrogramgraph and an electrocardiogram graph illustrated on the same time axis;

FIG. 28 is a graphic representation on a display device of identifiedlocations within a patient;

FIG. 29A is a chart showing next possible locations based on last knownposition;

FIGS. 29B-29C illustrate a flowchart for identifying a state or positionof a mapping catheter or leads;

FIG. 29C′ is a simplified flow chart showing next possible locationswithin a heart of an instrument based on last known locations;

FIGS. 30A-30B illustrate a dimensional change displayed on a displaydevice;

FIGS. 31A-31B illustrate a flow direction graph representation ofmovement on a display device;

FIG. 32 illustrates a mapping catheter with a flexible portion;

FIG. 33 illustrates a mapping catheter with a flexible portion,according to various embodiments;

FIG. 34A is a schematic view of a heart with a mapping catheter and aflexible portion, according to various embodiments;

FIG. 34B is a graphical representation of location information;

FIG. 35 is a representation of a display device illustrating a sheathedand unsheathed electrode; and

FIG. 36 is a flowchart for utilization of position data.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Thedevices described herein include an exemplary number of leads, casebodies, etc. One will understand that the components, including numberand kind, may be varied without altering the scope of the disclosure.Also, devices according to various embodiments may be used in anyappropriate diagnostic or treatment procedure, including a cardiac,neural, or other anatomical procedures.

Overview

As discussed herein, a navigation system, such as the navigation system20 illustrated in FIG. 1, can be used to navigate a procedure relativeto a patient 26. As discussed in detail herein, various instruments canbe moved relative to the patient 26 and tracked relative to the patient26. Although an image-guided system can include acquiring image data ofthe patient 26, such as with an imaging device 28, the imaging device isnot required, as discussed herein. A portion of the patient's 26 anatomycan be mapped by identifying a plurality of points within the patient 26by determining a relative location of an instrument. The plurality ofpoints can be illustrated individually, or sequentially, or a surfacecan be illustrated over or without the plurality of points to illustrateor identify a portion of the anatomy of the patient 26. The discussionherein may refer to map data or map data points and will be understoodto include individual acquired data points, illustrated individual ormanaged points an algorithm process applied to acquired data points toimprove visual display by eliminating regions of especially high densityand useful in modulating characteristics of rendered surfaces, arendered surface, or any appropriate manner of illustrating the acquiredmap data. Once the map has been created of the patient 26 or a portionof the patient 26, either with or without a surface rendered relative tothe individual points, a procedure can be guided or navigated using themap data. The map data can be generated without other imaginginformation, such as image data that might be acquired with afluoroscopic system, magnetic resonance imaging (MRI) System, computedtomography (CT) Imaging System, three-dimensional echo, ultrasound (2D,3D, or 4D), or other imaging systems such as the imaging system 28.

The map data that can be displayed, such as illustrated in FIG. 10, canbe used to identify various anatomical features. In addition,instruments can be navigated relative to the patient 26 using the mapdata. Identification of implants, ablation or cannulation procedures, orother procedures can be performed. Accordingly, a procedure can benavigated and performed substantially precisely with the generated mapdata. A display device can be used to display the map data and/orillustrate icons representing various portions or reference pointsrelative to the patient 26. For example, an icon can represent aposition of the instrument relative to the patient 26. In addition, themap data can be generated in a substantially three dimensional or evenfour dimensional manner. Accordingly, the display can include a threedimensional viewing, simulated three dimensional viewing, or even fourdimensional viewing, such as to illustrate a change in the patient 26over time.

The map data can be generated or acquired with any appropriate system.As discussed herein, a position sensing unit (PSU) can acquire multiplepoints of or within the patient 26. The PSU system can measure voltage,bioimpedance, acoustic (e.g., sound and ultrasound), time-of-travel,magnetic field strengths, or any appropriate characteristic.

It will be understood, however, that the navigation system 20 can beused to navigate a procedure relative to the patient 26 without usingimage data generated by another imaging system, such as a fluoroscopicimaging system, other than the PSU 40. Although image guided navigationis generally known in the art. The display can include the map datawhich includes one or a plurality of points that are determined orgenerated by tracking a position element or device within or relative tothe patient 26. The position element can be associated with, connectedto, or include an instrument that is tracked with any appropriatetracking system, such as a bio-impedance, electromagnetic, optical,acoustic, or other appropriate tracking system. As discussed furtherherein, the map data can be used to generate or render a surface to moreclearly or selectively illustrate or identify various anatomicalfeatures and locations within the patient 26.

With further reference to FIG. 1, the navigation or mapping system 20can be operated by a user 22 with an instrument 24 to map a selectedspace, such as a portion of the patient 26. The instrument 24 can alsobe navigated relative to the patient 26. The instrument 24 can be movedrelative to the patient 26 for various procedures, including lead (e.g.temporary or permanent implantable cardiac pacing leads, with insulatedwiring for stimulating and/or recording signals in or on the heart)placement relative to the heart, mapping of the heart, mapping of aselected organ of the patient 26, or guiding or navigating theinstrument 24 relative to any appropriate portion of the patient 26.

The navigation system 20 can include various components, such as theoptional imaging device 28. The optional imaging device 28 can include afluoroscope, such as a fluoroscope configured as a C-arm. The C-armfluoroscope can include an imaging section 30 and a x-ray emittingsection 32. The imaging device 28 can be controlled by a controller 34.Images acquired with the imaging device 28 can be displayed on a displaydevice 35 that is associated with the imaging device 28. It will beunderstood, however, that the separate display device 35 is notrequired. In addition, if the imaging device is an x-ray imaging deviceany radio-opaque portions will appear as a part of the image whenviewed, including the instrument 24. Further, other imaging systems,such as ultrasound, can be used to image the patient 26 and may alsoinclude information regarding instruments within the imaging field ofthe ultrasound transducer.

The controller 34 can control the imaging device 28 and can store imagesgenerated with the imaging device 28 or transmit data or receiveinstructions via a data transmission line 36 to or from a processorand/or memory, such as one that may be included in a workstation 38.While the optional imaging device 28 illustrated here is a fluoroscopicc-arm other imaging devices, such as CT, MRI, ultrasound, etc., can alsobe employed. Moreover, it will be understood that the communication line36 can be any appropriate communication line such as a wiredcommunication line, a wireless communication system, or any other datatransfer mechanism.

The navigation system 20 can further include a Position Sensing Unit(PSU) 40 as illustrated in FIG. 2. The PSU 40 can include an impedanceor Electrical Potential (EP) system. The PSU can be the LocaLisa®Intracardiac Navigation System as previously provided by Medtronic, Inc.of Minneapolis, Minn., USA. The PSU 40 can also include any appropriatetracking system such as an electromagnetic (EM) or optical trackingsystem. An exemplary EM tracking system can include the Stealthstation®Axiem® electromagnetic tracking system and an exemplary optical trackingsystems include the Stealthstation® TRIA® optical tracking system, bothsold by Medtronic Navigation, Inc. having a place of business inColorado, USA.

Bio-Impedance Position Sensing Unit

If the PSU 40 includes an EP tracking unit it can include a control ordriving unit 42 that includes one or more input or output connectors 44to interconnect with a plurality of current conducting or drive patchesconnected directly with the patient 26. The current patches can includepatches to create three substantially orthogonal voltage or current axeswithin the patient 26. For example, a first y-axis patch 46 a and asecond y-axis patch 46 b can be interconnected with the patient 26 toform a y-axis (such as an axis that is generally superior-inferior of apatient as illustrated in FIG. 2) with a conductive path such that theconducted current establishes a voltage potential gradient substantiallyalong this axis and between the patches 46 a and 46 b. A related y-axiscurrent flows from the first y-axis patch 46 a to the second y-axispatch 46 b substantially along the y-axis. Likewise, a first x-axispatch 48 a and a second x-axis patch 48 b can be connected with thepatient 26 to create a x-axis (such as an axis that is generallymedial-lateral of a patient) with a voltage gradient substantially alongthe x-axis between the patches 48 a and 48 d and a corresponding x-axiscurrent flowing between patches 48 a and 48 b. Finally, a first z-axispatch 50 a and a second z-axis patch 50 b can be connected with apatient 26 to create a z-axis (such as an axis that is generallyanterior-posterior of a patient) with a voltage potential gradientsubstantially along the z-axis between the patches 50 a and 50 b with acorresponding z-axis current flowing between the patches 50 a and 50 b.The three axes are generally formed to have an organ or area of interestthat the common intersection or origin of each of the axes x, y, z.Accordingly, the patches 46-50 can be positioned on the patient 26 toachieve the selected placement of the axes x, y, z relative to thepatient 26. Each of the patches 46 a-50 b can be interconnected with thePSU input/output (I/O) box 42, via a wire connection or otherappropriate connection at the ports 44.

The current applied between the related patches generates a small ormicro-current, which can be about 1 microampere (μA) to about 100milliamperes (mA), in the patient along the axis between the respectivepatch pairs. The induced current can be of a different frequency foreach of the related patch pairs to allow for distinguishing which axisis being measured. The current induced in the patient 26 will generate avoltage gradient across different portions, such as the heart, that canbe measured with a position element. The position element can be anelectrode, as discussed in further detail herein. The sensed voltage canbe used to identify a position along an axis (whereby each axis can beidentified by the particular frequency of the current being measured) togenerally determine a position of an electrode along each of the threeaxes. Although a voltage can be sensed, an impedance can also becalculated or measured to determine a location in a similar manner. Itwill be understood, that a sensing of voltage will not eliminate otherpossible measurements for position determination, unless specificallyindicated. As discussed further herein, the position of the electrodewith respect to each of the three axes can be used as map data to beillustrated on the display device 58. Position elements can beelectrodes within the patient and reference electrodes areinterconnected with the PSU I/O box 42 such that the signals areprocessed by high impedance circuitry so as to not load and distort thesensed signals.

In addition, reference patches can be interconnected with the patient 26for reference of guiding or mapping with the instrument 24 relative tothe patient 26. The reference patches can include a first referencepatch 52 a and a second reference patch 52 b. The placement of thereference patches 52 a, 52 b can be any appropriate position on thepatient 26, including those discussed further herein according tovarious embodiments. For example, the first reference patch 52 a can bepositioned substantially over the xiphoid process on the skin of thepatient 26 directly exterior to the xiphoid process of the patient 26.The second reference patch 52 b can be positioned substantially directlyacross from the first patch 52 a on a dorsal surface of the patient 26.

By positioning the reference patch 52 a at the xiphoid process of thepatient 26, the reference patch 52 a has relatively less motion withrespect to the heart than many other locations on the skin of thepatient 26. The heart 80 of the patient 26 is substantially static inposition relative to the xiphoid process. By positioning the referencepatches 52 a, b at these locations, respiration may be monitored bymeasuring the relative voltage or impedance difference between the tworeference electrodes 52 a,b using the PSU 40. As discussed herein,impendence or voltage measured between the two reference patches 52 a,bcan be used to determine a respiratory cycle and the portion of thecycle that the patient 26 is in. Also, the reference patches 52 a,b canbe used to assist in cardiac cycle monitory in a similar manner.

The PSU I/O box 42 can be interconnected with the workstation 38, via aconnection or data transfer system 56. The data transfer system 56 caninclude a wire transmission, wireless transmission, or any appropriatetransmission. The workstation 38 can receive signals, which can beanalog or digital signals, regarding voltages sensed by the referencepatches 52 a, 52 b and electrodes on the instrument 24. The signals canbe used to determine a relative location of the instrument 24 and todisplay the determined relative location on the display device 58. Thedisplay device 58 can be integral with or separate from the workstation38. In addition, various interconnected or cooperating processors and/ormemory can be provided to process information, each may be a part of theworkstation 38 or separate therefrom. The processors can process thesignals from the patches 46-52 and instrument 24 to determine theposition of the instrument 24, display the determined positions or otherdata on the display device 58.

The navigation system 20 can further include user input or data inputdevices such as a keyboard 60, a joystick 62, or a foot pedal 64. Eachof the input devices, 60-64 can be interconnected with the workstation38 or appropriate systems for inputting information or data into theworkstation 38. This information or data can include identifyingappropriate information, as discussed further herein, such as variouscomponents, or anatomic regions.

With continuing reference to FIGS. 1 and 2, with particular reference toFIG. 2, the multiple driving or voltage patches 46 a-50 b are used toconduct current in the patient to create voltage potentials within thepatient 26 that can be sensed by electrodes that are positioned on orwithin the patient 26. It will be understood that the driving patches46-50 can be positioned on the patient 26 at any appropriate locations,such as the locations described with the Local Lisa™ position sensingunit previously provided by Medtronic, Inc. of Minneapolis, Minn., USA.The PSU I/O box 42, can create voltages and generate a small currentalong the axes between the related patches. The current generated caninclude different frequencies along the different x, y, and z axes todistinguish the x, y, and z-axes.

The instrument 24 can include an electrode, as discussed further herein,which is able to sense the voltage generated within the patient 26 dueto the patches 46 a-50 b positioned on the patient 26. The sensedvoltage can be used to calculate an impedance of the tissue in thepatient 26 based upon the voltage potential gradient generated betweenthe respective pairs of patches and the corresponding current.Generally, the current is carried due to an electrolyte in the patient26, such as blood, interstitial fluid, etc. within a heart 80 and bodyof the patient 26.

Tracking References

As discussed further here, the calculated impedance or sensed voltagecan be used to determine a location of the electrode of the instrument24 relative to a selected reference, such as reference patch 52 a or 52b. The reference patches 52 a, 52 b can be positioned at any appropriateposition on the patient 26. As discussed above, the first referencepatch 52 a can be positioned substantially over the xiphoid process ofthe patient 26. The positioning of the first reference patch 52 a overthe xiphoid process of the patient 26 can limit movement of thereference patch 52 a due to respiration or cardiac movement. Thereference patches 52 a, 52 b can also be used for repeat or multipleprocedures at different times. For example, the reference patches can beused to reorient or register the mapping data 194 to the patient 26 at asecond time, such as during a later procedure. Therefore, the referencepatch 52 a can be a substantially fixed reference patch for referenceregarding the voltage generated by the PSU 40.

The second reference patch 52 b can be positioned substantially directlyacross the thickness of the patient 26 on a dorsal side of the patient26 from the first reference patch 52 b. The two reference patches 52 a,52 b can be on the same horizontal plane. The horizontal plane isperpendicular to the coronal or median planes of an anatomy. The secondreference patch 52 b can also be substantially fixed relative to thepatient 26, at least in part because it is positioned on the dorsal sideof the patient 26 and the patient is supine for the procedure of leadimplantation.

In addition, the second reference patch 52 b can be used to reorient orcontinue reference of the data acquired with the electrodes of theinstrument 24 if the first reference patch 52 a is removed. For example,during a procedure an emergency may require the removal of all of thepatches from a ventral side of the patient 26, including the firstreference patch 52 a. After the treatment of the emergency, however, thedata acquired with the instrument 24 can be reoriented relative to thepatient 26 or relative to the instrument 24 using the second referencepatch 52 b. Also, the second reference patch can be used to continuemapping and provide a reference even if the first reference patch 52 ais not repositioned. Accordingly, use of at least two reference patches52 a, 52 b can assist to reference the mapping data acquired relative tothe patient 26.

The PSU 40 including the several patches can inject a current into thepatient 26. The current that is injected can be a substantially stablecurrent that is not substantially changed over time. If the current issubstantially stable then a voltage can be measured with an instrumentor reference patch, as discussed herein and above, to be used indetermining a location of the instrument or the reference patch relativeto the axis on the patient 26. Alternatively, or in addition thereto, animpedance can be determined based upon a measured current that isinjected in the patient and the measured voltage with the instrumentreference patch. The impedance can, therefore, be used to determine alocation of the instrument or the referenced patch. Accordingly, it willbe understood that the position of an electrode, such as of aninstrument, can be determined based upon a relationship of Ohms Law bydetermining an impedance or measuring voltage within the patient or anyappropriate volume 26.

It will be further understood that the PSU 40 can be understood to be animaging system. The imaging system or image acquisition of the PSU 40,however, can be based upon the determination of multiple points withinthe patient 26 and illustrating or displaying the points or a surfacerelative to the points on a display device. The PSU 40 can be used alonewithout any other imaging devices. Other imaging devices may includethose that are external to the patient or positioned within the patientto generate a field of view, such as an MRI, CT or an ultrasound of thepatient.

In addition to electrodes being positioned on or near a xiphoid processof the patient 26, various reference electrodes can be positioned atother locations on the patient. For example, as illustrated in FIG. 2,other locations on the patient 26 can include positions superiorly, suchas exemplary reference patch 53 a, inferiorly, such as at theillustrated position of patch 53 b, or any appropriate quadrant such asan upper left or upper right, reference patch locations 53 c and 53 d.Each of the reference patches, including the xiphoid reference patch 52a and the other patches 53 a-53 d can include respective anterior andposterior patch pairs. In addition, each of the reference patch pairscan be connected to the PSU I/O box 42. Thus, measurements can be madewith the various reference patches 52 a-b and 53 a-d and provided to thePSU 40 of the navigation system 20.

As discussed above, the xiphoid reference electrodes 52 a, 52 b can beused for various purposes. For example, the xiphoid reference electrodes52 a, 52 b can be used to reference the position of the mapped data, asexemplarily illustrated in FIG. 10, with reference icon 52 a i relativeto the reference electrodes 52 a, 52 b. Similarly, the additionalreference electrodes 53 a-53 d can also be used to orient the map data.This can be useful for example, if the mapping or tracked instrument ismoved within the patient 26 and temporary localization or tracking islost, for example, if a connection is lost between the instrument andthe PSU I/O box 42. Upon reacquiring a signal between the instrument andthe PSU I/O box 42 the reference electrodes 52 a, 52 b, or any of theother reference electrodes 53 a-53 d can be used to reorient theillustrated map data relative to the tracked instrument and thereference electrodes 52 a-b, 53 a-d.

The reference electrodes, whether the xiphoid reference electrodes 52 a,52 b or the other reference electrodes 53 a-53 d can be illustratedrelative to the mapped data such as including the surface rendering 241.For example, the surface rendering 281 can represent a portion of theanatomy, such as a right ventricle. The xiphoid reference patch 52 a canbe positioned on the patient 26 at the xiphoid process which is at aselected physical location relative to the right ventricle of the heart80. Accordingly, the position of the reference electrode 52 a can beillustrated on the display 58 as a reference mark 52 a i. Accordingly,the reference electrodes, such as the xiphoid reference electrode 52 a,can be used as a tracked portion or illustrated icon on the imagedisplay 58. Similarly, the reference electrodes 53 a-53 d can beillustrated at specific locations relative to the map data on thedisplay device 58 to provide a reference for the displayed map datarelative to the patient 26. The reference electrodes, including thexiphoid electrode pair 52 a, 52 b and the other reference electrodes 53a-53 d can be tracked along or with the tracking electrodes 56 a-56 b.Such as the instruments that are tracked within the heart 80 of thepatient 26. Accordingly, the position of the various referenceelectrodes 52 a, 52 b, and 53 a-53 d can be tracked using the trackingor localization system PSU 40.

Reference patches can also be used to measure a voltage drop of thetissue patch interface. Patches driven with current have a voltage dropacross the electrode tissue interface. Using raw unreferenced voltageintroduces measurement error which is eliminated by use of a reference.The reference electrodes can be used to measure the voltage drop.

Mapping Catheter

With reference to FIG. 3, according to various embodiments, a mapping ornavigation catheter 100 can be used as the instrument 24. The mappingcatheter 100 can include various portions, such as a balloon orinflatable portion 102. The inflatable or expandable portion 102 can bepart of a catheter system, such as a Swan-Ganz Balloon Catheter Systemsold by Edwards Lifesciences REF: D97120F5 (5F)] and generally known inthe art.

The mapping catheter 100 can further include a sheath 104, which can bedeflectable. A lead or catheter defining a lumen 106 can extend throughthe sheath 104 and through the balloon 102. A tip or first electrode 108can be provided on a distal end of the catheter 106 and a ring or secondelectrode 110 can be provided on a proximal end of the balloon portion102. This can provide at least two electrodes to sense a voltage withinthe patient 26 when the mapping catheter 100 is positioned within thepatient and the current patches are being driven. As discussed furtherherein, the electrodes 108, 110 can sense a voltage produced within thepatient 26 and from the sensed voltage an impedance can be calculated todetermine a location of the mapping catheter 100, as discussed furtherherein.

In addition, during mapping, the balloon portion 102 can assist inassuring that the catheter 106 does not puncture, lacerate or perforatea wall of the heart 80 or other blood vessel. The balloon portion 102can also act as a stop when the mapping catheter 100 is being movedthrough the heart 80 or other anatomical portion. The balloon portion102 can be inflated or deflated as selected by the user 22. Inflation ofthe balloon portion 102 can be performed in any appropriate manner suchas directing a fluid, such as a liquid or gas, through the catheter 106.In addition, the mapping catheter 100 can be moved relative to thepatient 26 in any appropriate manner, such as a steering mechanism (notparticularly illustrated) or via anatomical forces placed upon variousportions of the catheter 100, such as a drag created on the balloonportion 102 by the flow of blood. Further, various conductors can beused to transfer the sensed voltage from the electrodes 108, 110 to thePSU I/O box 42.

Lead Instrument

With reference to FIG. 4, a lead 120 is illustrated that can also beused as the instrument 24. The lead 120 can be any appropriate lead suchas the model 5076 sold by Medtronic, Inc. of Minneapolis, Minn., USA.The lead 120 can be used as part of an implantable medical device 300(illustrated in FIG. 13), but need not generally be used to acquiringmapping data. The position of the lead 120, can be determined anddisplayed on the display device 58, as discussed further herein. Thelead 120 can include an external sheath or covering 122 thatsubstantially insulates an interior of the lead 120 from an externalenvironment, such as an anatomical portion. The lead 120 can include aconductor 124 and a retractable helix electrode 126. The electrode 126can be used with the PSU 40 to determine the location of the electrode126. However, generally during insertion and placement of the lead 120,the electrode 126 is substantially retracted into the covering 122 ofthe lead 120. Accordingly, an appropriate or strong signal of thevoltage may not be efficiently determined in the retracted state. Thismay be because the signal may have high source impedance when theelectrode is retracted and voltage measurements may be misleading.Therefore, an opening, which can include one or more portals or windows128 a, 128 b can be formed in the covering 122 to allow an electrolyteto contact the electrode 126 while moving the electrode 126 through thepatient 26. A voltage can be efficiently sensed by the exposed electrode126 through the window portions 128 a, 128 b.

As discussed herein, the determined position of the lead 120 can beillustrated on a display device relative to data collected either withthe lead 120 or with the mapping catheter 100. Accordingly, the sensedvoltage through the window 128 can be used to determine a position ofthe lead 120 relative to the mapping data. It will also be understood,the lead 120 may include more than the implantable electrode 126. Thelead 120 may include at least a second electrode, such as a ringelectrode 127. A voltage can also be sensed by the ring electrode 127and also be used for determining a position of the lead 120 or a portionthereof.

Catheter Opening or Passage

With reference to FIGS. 4A and 4B, a lead 140, according to variousembodiments, can include a moveable window covering portion 142. Thecover 142 can move with the electrode 126 as the electrode 126 is movedout of the covering sheath 122. As illustrated in FIG. 4A, when in theretracted configuration the windows 128 a, 128 b are uncovered to allowan electrolyte to contact the electrode 126 over a large surface areawhich lowers impedance of the circuit. As illustrated in FIG. 4B, whenin the extended configuration the windows 128 a, 128 b are covered bythe window covering 142 which blocks access to the electrode 126 thoughthe widows 128 a, 128 b.

Accordingly, the cover 142 can move from a non-covering or openedposition to a covering position relative to the window 128 when theelectrode 126 is deployed or extended. The cover 142 can cover thewindow 128 to ensure that a material, such as blood or other materialdoes not enter the cover 122 after extension of the electrode 126. Itwill be understood that providing the cover 142 may not be necessary forappropriate operation of the lead 120 with an implantable medicaldevice.

Display Map Data Points

With reference to FIGS. 1-3 and further reference to FIGS. 5 and 6, aselected map data 194 of an anatomical region, such as a heart 80 can beproduced. The map data 194, as illustrated in FIG. 6, can be generatedusing only the PSU 40. Thus, the map data 194 can be considered withoutreference to an external imaging device or other imaging device. Asurface or virtual image, however, can be generated as discussed herein.

As discussed above, the heart 80 includes an electrolyte, such as blood,which can be used to allow the sensing of a voltage or bio-impedancewith an electrode, such as the electrodes 108, 110 of the mappingcatheter 100 or electrode 126 of the lead 120. The voltages sensed bythe electrodes 108, 110 are generated by the currents conducted throughpatches 46 a-50 b, as particularly illustrated in FIGS. 1 and 2 andremoved from FIG. 5 for clarity. The patches positioned on the patient26 create virtual axes within the patient 26 of induced voltagegradients. A determination of a position of the electrode can be made bysensing the voltages or determining impedance within the patient whilethe current is conducted in the patient 26. The particular voltage orimpedance sensed or determined is based upon a location of an electrodein the patient 26. The electrodes 108,110 of the mapping catheter 100can sense the voltage of each of the three axes to determine a threedimensional position of the mapping electrodes 108, 110 within thepatient 26. Similarly, the electrodes of the leads 120, 140 can be usedto sense the voltages in the three axes to determine the position of theelectrodes within the patient 26. The mapping catheter 100, includingthe electrodes 108, 110, can be moved through various portions in thepatient 26 while the electrodes sense the voltages, substantiallycontinuously or as selected, among the three axes to determine multiplethree dimensional positions of the electrodes.

A selected number of position measurements or determination can be made,such as manual selection or automatic selection at selected timeintervals. The sensed voltages can then be used to determine a relativeposition of the electrodes, as discussed herein. In addition, such aswhen the two electrodes 108, 110 are provided, a direction of thecatheter 100 can also be determined. For example, a location of both ofthe electrodes 108 and 110 can be made. Based upon this determination adetermination of direction of the catheter 100 or orientation of thecatheter can be made based upon the two location or positiondeterminations. It will be understood, that a similar directiondetermination can be made regarding any appropriate catheter with atleast two electrodes positioned along its length.

As discussed above, the mapping catheter 100 can include the Swan-Ganzcatheter which can include a syringe or similar device 150 to inject afluid or gas to inflate the balloon 102. A pressure meter or sensor 152can also be interconnected with the lead that is within the balloon 102to sense a pressure placed on the balloon 102 when the balloon is withinthe patient 26. For example, once the balloon 102 is inflated, such aswhen the balloon 102 is positioned exterior to the sheath 104, apressure induced on the balloon 102 will be transmitted through thecatheter 106 and can be measured with the pressure meter 152. It will befurther understood, however, that a pressure meter or transducer canalso be positioned at any appropriate location, such as within theballoon 102. As discussed further herein, the measurement of a pressurepulse or a pressure change can be used to identify various regions ofthe heart 80 by the user 22. In this regard, an increase or change inpulsative pressure can be used to identify regions of the heart such asthe right atrium, right ventricle, pulmonary artery, and the locationsof valves.

The mapping catheter 100 can be introduced into the patient 26 via anyappropriate method to collect map data. Returning reference to FIG. 5A,the catheter 100 can be positioned in a vein 144 of the patient 26through an incision 146 made in the dermis of the patient 26 and anintroducer 145. Other appropriate mechanisms can also be used tointroduce the mapping catheter 100 into the vein 144. The introducer 145can be any appropriate introducer, such as the introducer HLS-1007 soldby Pressure Products, Inc. having a place of business in San Pedro,Calif., USA. The introducer 145 generally provides a semi- orsubstantially rigid opening for introducing or moving the catheter 100into the patient 26. The introducer 145 can include an opening thatincludes a diameter of a selected dimension larger than an externaldiameter of the catheter 100. The opening in the introducer 145 cangenerally be defined a throughbore or cannula extending from a first endto a second end of the introducer 145. An instrument, such as themapping catheter 100, can be passed through the instrument introducer145.

The introducer 145 can be tracked relative to the patient and to themapping catheter 100 with any appropriate mechanism. For example, theintroducer 145 can include an electrode 145 a that can be tracked orhave its position determined by the PSU 40. As discussed above, theposition of the mapping catheter 100 can be identified or determinedwith the PSU 40 using a measured voltage or impedance at the electrode.The electrode 145 a of the introducer 145 can operate substantiallyidentically and have its position determined with the PSU 40.

It will be understood that any appropriate tracking system, however, canalso be used to track the location of the introducer 145. For example,an electromagnetic, optical, acoustic, or any appropriate trackingsystem can be used to track at least a portion of the introducer 145. Asillustrated in FIG. 5A, a tracking device 147 can be interconnected withthe introducer 145. Tracking the tracking device 147 can allow for adetermination of a position of the introducer 145 relative to thepatient 26 using a tracking system that can be separate or additional tothe PSU 40.

Various navigation or tracking systems can include those disclosed inU.S. Patent Application Publication No. 2008/0132909, assigned toMedtronic Navigation, Inc., and incorporated herein by reference.According to various embodiments, image data of the patient 26 can beacquired prior to a procedure and the image data can be registered tothe patient 26 according to appropriate methods and with appropriatedevices. Therefore, the introducer 145 including the tracking device 147can be tracked and navigated, such as with the image data of the patient26, to position the introducer 145 at a selected location relative tothe patient 26. Also, the introducer 145 can be navigated relative tothe map data 194 generated of the patient 26.

With initial reference to FIG. 7, a procedure 180 is illustrated thatcan use the position sensing unit 40, its associated patchesinterconnected with the PSU I/O box 42, the mapping catheter 100, andthe lead 120 to map and determine a position of the lead 120 in thepatient 26 without the need to employ an external imaging device. Theprocedure 180, as briefly discussed here, can include creating a map ofa portion of the patient 26 and positioning leads within a portion ofthe patient 26. It will be understood that although the procedure 180 isdiscussed relating to a cardiac procedure, other appropriate procedurescan be performed by positioning the mapping catheter 100, currentpatches and reference electrodes in different portions of the patient26. For example, a map can be made of other areas, such asgastrointestinal areas, pleural areas, or other areas of the anatomy ofthe patient 26 including an electrolyte material. Accordingly, theprocedure 180 can be modified in an appropriate manner to be used withan appropriate procedure.

The procedure 180 can start in start block 182. The procedure 180 canthen proceed to preparing and configuring the position sensing unit anda display device, as illustrated in FIG. 1. Preparing the PSU in block184 can include various steps, such as labeling the patches forpositioning on the patient 26, interconnecting the patches with the PSUI/O box 42, the workstation 38 with the PSU I/O box 42, and otherappropriate steps.

After the PSU 40 is prepared in block 184 and the patches 46 a-50 b canbe positioned on the patient 26 in block 186. In addition, the referencepatches 52 a and 52 b can be positioned on the patient 26 as well inblock 186. The patches 46 a-52 b can be positioned on the patient 26 asillustrated in FIGS. 1 and 2. Positioning of the patches on the patient26 allows for the position sensing unit 40 to generate potentials withinthe patient 26 that can be sensed with the electrodes 108, 110 of themapping catheter and electrodes of the lead 120. The patches 46-52 canbe attached on a skin surface of the patient 26. This can allow forefficient generation of the current in the patient 26.

The current can be any appropriate amount. For example, the currentinjected along the various axes can be about 1 μA to about 100 mA. As aspecific example, the current may be a current that is about 1 μA. Sucha micro-current, however, may not always be injected exactly at 1 μA,but may vary by 1%, 2%, 5% or any acceptable percentage. Determining animpedance may assist in obtaining a precise or accurate position.Determining an impedance is based on a sensed voltage at a known ormeasured current. Also, determining an impedance rather than a voltagemay adjust and account for differences in current between the threeorthogonal axes. Thus, a changing or inconstant current can be used todetermine a precise impedance for position determinations. Generallyboth sensing a voltage and/or determining an impedance can be referredto as evaluating an electrical property, such as for positiondetermination.

The display device 58 and its associated controller or processor canthen be adjusted to illustrate or display a right anterior oblique (RAO)and a left anterior oblique (LAO) view in block 188 and as particularlyillustrated in FIG. 6. The two oblique views can illustrate for the user22 views of the data mapped of the patient 26 that can be generallysimilar to fluoroscopic or x-ray images otherwise acquired of thepatient 26. However, because no imaging device is necessary to form theimages, the view of the patient 26 or access to the patient 26 is notobstructed by the imaging device 28. As illustrated in FIG. 6, a legendcube 98 can be used to identify the view angles being represented. Asdiscussed above, the use of the mapping catheter 100 and the positionsensing unit 40 can eliminate or substantially reduce fluoroscopicimaging of the patient 26, while maintaining an appropriate level oflocation identification of various portions, such as the lead 120 withinthe patient 26. It will be understood, however, that any appropriateviewing angles can be displayed on the display device 58, the obliqueviews are merely exemplary.

Display Reference

Even with a reference cube and known display orientation, reference to aphysical location of the patient 26 can be useful for orienting thedisplay 58 to the patient 26. Thus, the display 58, shown in FIG. 6 canalso be used to selectively display information in addition to themapping and data points 198. Icons 46 a′, 46 b′ can show the pseudolocation of the axes patches of the PSU 40. The pseudo location of thepatches shown by icons 46 a′, 46 b′ or other patches can be based uponrelative positions of the axis patch electrodes 46 a-50 b. That isbecause the axis patch electrodes 46 a-50 b inject current and are notinputs into the PSU 40 so that their position can be determined with thePSU 40. The patch electrodes 46 a-50 b are positioned on the patient 26according to an appropriate manner. For example, as illustrated in FIG.2 above, the patches can be positioned on the patient to generate axisx, y, and z currents. The patches 46 a-50 b that are positioned on thepatient 26 can also be used to orient the data illustrated on thedisplay 58. For example, the user 22 can select to illustrate or showthe patches on the display 58.

As illustrated in FIG. 6, selected patches can be displayed. To betterillustrate the orientation of the data on the display device 58 relativeto the patient 26, the user 22 can select to have the icons 46 a′, 46 b′displayed to represent the relative physical location of the patches 46a, 46 b. Because the patches 46 a, 46 b are physically on the patient26, the user 22 can be oriented on the display device 58 relative to thepatient 26. It will be understood that the PSU 40 can have an input toallow the user to select to show the patches as icons on the display 58or not show the patches as icons on the display 58.

The position of the patches illustrated as icons on the display 58, suchas the two patch icons 46 a′ and 46 b′ can be determined based upon theposition of the map point data 198. As discussed herein, the map pointdata 198 is determined by measuring a voltage or bioimpedance based upona current generated between pairs of patches 46 a-50 b. Accordingly, thedetermination of the location of the electrode being used to measure thevoltage can also be used to determine the position of the patchesrelative to the measured voltage for determining an appropriate locationfor illustrating the patch icons on the display 58. In a similar manner,the relative positioning of the reference electrodes 52 a,b can be shownas icons 52 a′, b′ on the display 58.

Returning reference to FIG. 7 of the collection of the map data isfurther discussed. The mapping catheter 100 can be prepared in block190. For example, the catheter 106 can be marked relative to the sheath104 for illustrating the position of the balloon 102 necessary toposition the balloon 102 and electrodes just free of the sheath 104.This is generally a sterile procedure, and can be performed in anappropriate sterile manner.

The mapping catheter 100 can then be inserted or introduced into thepatient in block 192. It will be understood that the mapping catheter100 can be introduced into the patient 26 in any appropriate manner.Upon introduction into the patient 26, plotting of data points with themapping catheter 100 can begin in block 192. The plotting of the datapoints can include illustrating data points on the display device 58,illustrated in FIGS. 1 and 6. The data points can be acquiredsubstantially continuously or at a selected rate. The plotting of thedata points can produce mapping data 194 that can be illustrated in anyappropriate manner, such as a plurality of points 198 on the displaydevice 58. The plurality of points illustrated on the display device 58can be produced by moving the mapping catheter 100 through the heart 80,the veins of the patient 26, and other appropriate portions or movingmechanisms.

For example, once the balloon 102 has been inflated, drag is induced onthe balloon 102, due to the flow of blood in the patient 26. This canassist the balloon 102 to move generally in the direction of the flow ofblood in the patient and allow for ease of movement and guiding of theballoon catheter 100 within the patient 26. For example, the ballooncatheter 100 can be introduced into the patient 26 and the flow of bloodcan direct the balloon catheter 100, from the right ventricle throughthe right ventricular outflow tract and into the pulmonary artery.

As illustrated in FIG. 6, the display device 58 can display a pluralityof points that are acquired as the mapping catheter 100 is moved throughthe various portions of the patient 26. The plurality of points as thecatheter 100 is moved through the patient, which is generally over time,allows for the creation of a map of the portion of the patient 26through which the mapping catheter 100 is moved. As exemplaryillustrated in FIG. 6, the display device 58 can illustrate the acquiredmapping data 194 to illustrate appropriate portions of the heart 80.

The map data points 198 illustrated on the display device can also bemanaged for ease and efficiency of the user 22. For example, a selecteddensity of data points 198 can be selected. Once a density threshold isreached a representative data point can be illustrated on the displaydevice 58 rather than all acquired map data points that have beenacquired with the mapping catheter 100. In other words, a representativedata point 198 may actually represent more than one acquired positionmap point allowing fewer than all acquired position data points to beillustrated, but all can be used for rendering a surface, as discussedfurther herein. This can allow the map data 194 display to beselectively uncluttered with multiple overlapping map data point icons198.

Landmarks can be identified in block 193 for display on the displaydevice 58. Landmarks identified in block 193 can be any appropriatelandmark and can be illustrated such as with a toroid 204 or a selectedpoint, such as a point of a different color or shape 206 in the mappingdata 194. The landmarks identified in block 193 can be any appropriateanatomical feature used as a landmark for a procedure. For example, ananatomical feature or landmark can include an ostium or opening, avalve, wall, or apex of the heart 80 or other portions of the patient 26being mapped with the mapping catheter 100. The landmarks or furtherlocations can be further limited based upon a determination of only thepossible subsequent locations of the electrodes of the mapping catheteror lead. For example, from within the pulmonary artery the mappingcatheter 100 or lead 120 can generally only move back into the rightventricle. Accordingly, the mapped points or the information regardingthe same can be provided to the user 22 to limit the possible further ornext positions.

The landmarks can include, as illustrated in FIG. 6, a first toroid 204a representing a junction of the inferior vena cava and the rightatrium, a second toroid 204 b representing a tricuspid valve, a thirdtoroid 204 c representing a pulmonic valve, and a fourth toroid 206 drepresenting a junction of the superior vena cava and the right atrium.Other icons can also be used to represent landmarks, such as a triangle206 that can represent an apex.

As various portions of the data are being acquired, the perspective orposition of the virtual camera on the display device 58 can be changed.For example, during initial plotting of the data an auto-follow positioncan be illustrated, as selected in block 195. The auto-follow positionallows the primary electrode or the electrode being tracked or themapping electrode to remain at the center of the display device. Theauto-follow position can move the virtual camera as illustrated on thedisplay device 58 based upon speed of movement of the electrode beingtracked or the location of the tracked or primary electrode relative tothe position of the virtual camera. Thus, the view on the display device58 can be based upon the position of the electrode relative to thevirtual position of the camera.

The auto-follow feature can keep the tip of the primary electrode as thecenter of focus on display device 58. Rather than allowing the cameraview to jump to wherever the electrode tip happens to be at a givenpoint in time, the method works by smoothly transitioning to that point.The rate of the transition is dependent upon the distance between thecurrent center of focus and the desired center of focus (the tipelectrode's location). The set of rules define how the center of focusgets updated and can include moving the camera view at a speedproportional to distance to the tip or moving it immediately to the newdesired position if the point of current focus is close to the newdesired focus. These rules allow the transition to be rapid whennecessary, while avoiding unnecessary and exaggerated movement when thecamera is close to being centered.

At a desired point, the auto-follow position can be discontinued inblock 196. When discontinued the view of the mapping data 194 can remainunchanged on the display device 58 as the electrode, such as theelectrode 126 of the lead 120, is moved through the heart 80 and itsrelative position is displayed on the display device 58. The auto-followfeature, however, can be restarted to maintain the tracked position ofthe electrode near a center of the display device 58. Further landmarkscan be identified in block 197 during or after any portion of the mapdata acquisition, such as after the tricuspid valve has been past orobserved.

At an appropriate time a rendering of one or more of a point 198 in themapping data 194 can be produced in block 200. The rendering can includea 3D rendered surface using the data points 198 in the mapping data 194.The mapping data 194 can be rendered, as discussed further herein, toillustrate or form a surface on the points 198 or relative to the points198. The rendered data can be used to illustrate the mapping data 194for appropriate purposes.

The map data can be rendered at any appropriate time. A user 22 canselect that an appropriate amount of data has been selected orillustrated. Alternatively, or in addition to manual selection, the PSU40 or other appropriate automatic processor can render a surface whenappropriate amount of map data is collected with no additional inputfrom the user 22.

Once an appropriate amount of data has been acquired and illustrated onthe display device 58, a selected procedure can use the mapping data 194acquired from patient 26. For example, various leads can be positionedwithin the patient 26, such as in a right ventricle or in a rightatrium. Therefore, the procedure 180 can exemplary include configuring aRV lead in block 202. Configuring the RV lead in block 202 can includeinterconnecting the RV lead with the PSU I/O box 42 for guiding the RVlead, such as the lead 120, to a selected point in the patient 26 andconfiguring the PSU 40 to illustrate and display the RV lead as it isintroduced and navigated through the patient. For example, asillustrated in FIG. 6, a graphical representation 120′ of the lead 120can be displayed relative to or superimposed on the mapping data 194.Illustrating a graphical representation of the lead 120 can allow theuser 22 to understand the position of the lead 120 relative to themapped data of the patient 26. The representation of the lead 120′ canbe displayed relative to the data points 198. For example, the datapoints can represent a 3D volume; accordingly the lead representation120′ may be partly obscured by some of the data points 198. Therepresentation of the mapping data 194, however, can be rotated asselected by the user 22 to view the mapping data 194 and the leadrepresentation 120′ in any appropriate selected manner.

It will also be understood that the mapping catheter can be removed fromthe patient 26 prior to positioning the lead 120 in the patient 26. Theprocedure 180 can then proceed to placing and testing the RV lead in thepatient 26 in block 206. Placing and testing the RV lead can proceedaccording to generally known methods such as for placing leads forpacing or defibrillation IMDs. In addition, configuring a RA lead inblock 208 and placing and testing a RA lead in block 210 can alsofollow. It will be understood, however, that any appropriate procedurecan be performed and a cardiac procedure is merely exemplary. Inaddition, any appropriate type of lead or number of leads can bepositioned within the heart 80 of the patient 26 for a selectedprocedure.

At a selected point, such as after the leads are positioned and tested,an option image can be obtained by an external imaging device in block211. The external imaging device can include the fluoroscope 28 or otherappropriate external imaging system. The minimal or single imageacquired by the imaging device can substantially reduce exposure tox-rays or the requirement of equipment usage.

The procedure 180 can then end or terminate in block 212. The ending ofthe procedure can include appropriate steps, such as programming an IMDpositioned within the heart, as illustrated in FIG. 13 connectingimplanted leads to the IMD, closing the incision, implanting theimplantable medical device, or other appropriate steps. Programming theIMD can include wireless programmer, such as using the Medtronic 2090 orCarelink™ programmer, provided by Medtronic, Inc. of Minneapolis, Minn.,USA.

Electrode Patch Positioning

With reference to FIGS. 1 and 2, the electrode patches 46 a-50 b thatare prepared in block 184 and placed in a patient in block 188 can beany appropriate patches, such as the patches and controller of the LocalLisa™ previously sold by Medtronic Inc. of Minneapolis, Minn., USA. Asan example, the LocaLisa® device can be used to generate the current inthe patient 26. The PSU 40 can also be that disclosed in U.S. Pat. Nos.5,697,377 or 5,983,126 to Wittkampf, incorporated herein by reference.It will be understood that any appropriate number of axes patches can beused, but the six disclosed herein can limit issues with sterile fieldmaintenance and allow reasonable access to the patient 26 during aprocedure. The patches can be positioned on the patient 26, such asorthogonally or generally nearly orthogonally to one another, to createthree orthogonal or generally nearly orthogonal axes within the patient26, and particularly intersecting within the heart 80 or other organ ofinterest of the patient 26. The patches 46-50 can be oriented based uponthe organ or region of interest in the patient so that the original isat the region of interest. In addition, various instruments can be used,such as of different size or configuration, based upon the organ beingexplored or mapped.

The applied patches 46, 48, and 50, can each be used to conduct asubstantially unique current waveform through the patient 26. Forexample, each pair of the patches can be used to conduct current at adifferent frequency. Alternatively, the currents could be time divisionmultiplexed. Thus, the PSU 40 can be used to generate the uniquecurrents in the patient 26. The currents generated in the patient 26produce voltages that can be sensed with the electrodes, 108, 110 of themapping catheter 100 or the lead 120, to be used to determine theelectrode's relative position in the patient 26.

The reference electrodes 52 positioned on the patient 26 can be used toas a reference electrode for the electrodes being used to sense avoltage in the patient 26. The reference electrode 52 a that ispositioned over the xiphoid process can remain substantially fixedrelative to the patient 26 Reference electrodes positioned on thepatient 26 provide a reference for determination of voltages by theelectrodes 108, 110 of the mapping catheter 100 within the patient 26.

As discussed above, at least one of the reference electrodes, such asthe first reference electrode 52 a, can be positioned substantially onor over the xiphoid process of the patient 26. Positioning the referencepatch 52 a substantially near the xiphoid process of the patient 26 canallow for a substantially fixed location of the reference patch 52 arelative to the patient 26 regardless of respiration movement, cardiacmovement, or the like of the patient 26. Also, as discussed above,positioning the second reference electrode 52 b substantially directlyacross from the first reference electrode 52 a (such as on a horizontalplane, as discussed above) can provide a second reference that can beused to reference the mapping data 194 generated or produced relative tothe patient 26. Also, by positioning the second reference patch 52 b atthis location relative to the first reference patch 52 a, respirationcan be monitored by measuring the relative voltage or impedancedifference between the two reference patches 52 a, 52 b using the PSU40.

The various patches can be affixed to the patient 26 in any appropriatemanner, such as via generally known semi-permanent or permanentadhesives. The patches 46-50 are also generally electrically coupled tothe skin of the patient 26 to allow current to be conducted within thepatient 26. For example, the patches 46-50 can be directly attached to askin surface of the patient 26. The patches 46-50, however, can beremoved once mapping or other procedures are completed.

Enabling plotting in block 192 allows for generation of the multipledata points for generation of the mapping data 194 of the patient 26 andmapping of selected regions of the patient 26, such as the heart 80. Themapping of the heart 80 of the patient 26 can be achieved by moving themapping catheter 100 through selected portions of the heart 80 of thepatient 26. It will be understood, as discussed above, that anyappropriate region of the patient 26 can be mapped. Moving the mappingcatheter 100 through the heart 80 of the patient 26 allows forgeneration of the mapping data 194 based upon a plurality of sensedvoltages and calculated impedances at multiple locations within theheart 80 by the electrodes 108, 110 of the mapping catheter 100. As themapping catheter 100 moves through the heart 80 of the patient 26, asexemplary illustrated in FIG. 5, data points can be acquired at a setinterval of time or when selected by the user 22. The user 22 can usethe foot pedal 64 to determine when a data point is to be acquired orfor selecting where a landmark should be illustrated and identified.Nevertheless, the movement of the mapping catheter 100 through the heart80 allows for collection of data points based upon sensing a voltageand/or calculating an impedance at multiple locations in the heart 80.

Managed Points

For example, as illustrated in FIG. 5, as the mapping catheter 100 movesthrough the heart 80, it can be positioned at different locations withinthe heart 80. For example, as it enters the right atrium chamber of theheart it can be positioned in a first selected location, as illustratedby the phantom mapping catheter 100′. A data point can be determined forthe mapping catheter when it is at position 100′. The mapping cathetercan further be moved through the heart 80 such as to a second or thirdlocation, as illustrated at 100 or 100″, and data points can be furtheracquired at these additional locations. Although three points arespecifically mentioned here, it will be understood, that any appropriatenumber of data points may be collected to form the mapping data 194, asillustrated in FIG. 6. These data points can be illustrated on thedisplay device 58 as the data points 198. As also illustrated in FIG. 6,a plurality of data points 198 can be generated or acquired as themapping catheter 100 is moved relative to the patient 26. It will alsobe understood that any appropriate number of data points 198 can bedisplayed on the display device 58.

The data points 198 can be represented individually or as a group. Forexample, a selected sphere, circle, or other appropriate geometric shapecan be used to represent one or more acquired data points 198 of aposition of the mapping catheter 100, or its respective electrodes 108,110, within the patient 26. A single sphere data icon (or managed point)illustrated on the display device 58 can be displayed when two, three,or more data points have been collected for a respective voxel of themapping data 194. Therefore, a single data point representation 198 onthe display device 58 can be representative of one or more position datapoints acquired with the mapping catheter 100. Accordingly, the imagedisplay 58 can be densely or sparsely populated with representations ofthe position data points of the mapping catheter 100. The representationcan be based upon a selection of the user 22 or other appropriateselections.

In addition, the mapping catheter 100 can move through the heart 80according to various forces. For example, the sheath 104 of the mappingcatheter 100 can be a substantially deflectable or guidable sheath.Additionally, the mapping catheter 100 can be guidable according togenerally known techniques or processes. Therefore, the mapping catheter100 can be moved through the patient 26 by direction of the user 22. Inaddition, forces within the patient 26, such as the flow of blood, canbe used to move the mapping catheter 100 through the heart 80.

The balloon portion 102 can generate drag within the patient 26 due toblood flow or other fluid flows within the patient 26. Therefore, asillustrated in FIG. 5, the mapping catheter 100 can enter the heart 80at a selected location and be moved through the heart 80 via drag formedon the balloon portion 102 to assist in moving the balloon portion 102,and the associated electrodes 108, 110, through the heart 80 such as toor through the pulmonary artery. Therefore, the mapping catheter 100 canmove relative to the patient 26 in any appropriate manner, including adrag generated on the balloon portion 102.

Landmarks

With continuing reference to FIGS. 2, 5, and 7 and further reference toFIG. 8, the catheter 100 can be moved through the heart 80. As thecatheter 100 is moved through the heart 80, the position sensing unitsystem 40 can determine or calculate positions of the electrodes 108,110 of the mapping catheter 100. Each of these determined locations canbe displayed on the display device 58, as illustrated in FIG. 8, asvarious data points including 198 a and 198 b. Each of the data pointscollected regarding a position of the mapping catheter 100 can alsoinclude a time stamp or cycle stamp. Therefore, for example, a firstdata point 198 a and a second data point 198 b can include differenttime stamps. The time stamps can indicate which was acquired first asthe mapping catheter 100 moved relative to the heart 80. As discussedabove, drag on the balloon portion 102 can cause movement of thecatheter 100 through the heart 80.

Accordingly, a movement direction can be determined and illustratedbased upon the calculated or determined locations over time of themapping catheter 100. An arrow 199 can also be illustrated on thedisplay device 58 to represent the movement direction. The arrow 199 canprovide an indication to a user 22 of the movement direction in theheart 80 and can assist in determining landmarks.

In addition, as the mapping catheter 100 is moved through the heart 80,as illustrated in FIG. 8, pulsative pressure exerted on the balloonportion 102 can be measured with the pressure meter 152 to determine apressure pulse exerted on the balloon portion 102. The pressure pulsecan be illustrated as a wave form that can be used to assist inidentifying various locations in the heart 80, or other locations in thepatient 26. The measured waveform may be low fidelity due tocompressible gases and also due to the use of a small lumen in the lumen106 of the catheter 100, but may be of enough fidelity to identifyanatomical landmarks or portions. As the data points are collectedregarding the location of the mapping catheter 100, in particular theelectrodes 108, 110, a pressure pulse related to these positions canalso be determined. The workstation 38 can save or associate each of thepressure pulses with the data points regarding the location of themapping catheter 100 when the pressure pulse was measured. Accordingly,each of the data points 198 of the mapping data 194 can includeinformation collected with the mapping catheter 100. In addition, themapping catheter 100 can be used for electrogram recording and display.For example, equal atrial and ventricular contributions to theendocardial electrogram could help confirm a location proximal to thetricuspid or pulmonic valves. Therefore, each of the data points 198 ofthe mapping data 194 can have information associated therewith otherthan a position of the catheter 100.

The additional information can be used in conjunction with the positioninformation to assist in identifying various regions of the heart 80,such as landmarks. For example, different portions of the heart, such asvalves, chambers and the like can be identified using the electrograms,pressure information, and the like. This information, which isassociated with the data points 198, can be used to identify landmarksin the mapping data 194 of the heart 80. Accordingly, as illustrated inFIG. 6, the landmarks can be illustrated on the display device 58 toassist a physician in identifying or recalling selected regions of theheart 80 determined with the mapping catheter 100. The landmarks 204,206 can be identified using the physician's knowledge, informationcollected from the mapping catheter 100, and information collected fromother instruments such as an electrocardiogram (ECG).

The landmarks can be labeled on the display device 58 in an appropriatemanner. Landmarks displayed and labeled on the display device 58 caninclude a label line 220 that interconnects the landmark 204 with a textbox 222. The length of the lead line 220 and the position of the textbox 222 can be calculated to ensure that the position of the text box222 does not obscure or obscures as few as possible the data points 198displayed on the display device 58. In addition, the labeling of thelandmarks 204, 206 or the identification landmarks that should belabeled or identified can also be done with the foot pedal 64 and/or thejoystick 62. For example, depressing the foot pedal 64 can be used toshow a menu of possible landmarks and the joystick can be used tohighlight the landmarks and the foot pedal 64 can select a landmarklabel. The workstation 38 can then illustrate the landmark on thedisplay device 58 and further provide the text box label 222 and thelead line 220 in an appropriate manner.

Returning reference to FIGS. 6 and 7, identification of landmarks inblock 202 can be illustrated on the display device 58 as brieflydiscussed above. Selected landmarks, such as the cannulum of valves,ostia of veins or vessels, can be illustrated using the toroid 204. Thetoroid landmark 204 includes a radius centered on an axis 204′. The axis204′ and a radius of the toroid 204 can be based upon the data points198 acquired near the toroid 204 or the location of the landmark whichthe toroid 204 identifies. For example, a selected portion of the datapoints 198 near the toroid 204, such as one or two or any appropriatemillimeters on either side of the toroid 204 can be used to determinethe direction of the central axis 204′ for display on the display device58. In addition, the data points 198 within the toroid 204 can be usedto determine the radius of the toroid 204 for display on the displaydevice 58. Therefore, the landmark toroid 204 can, in addition toidentifying a selected landmark, also provide additional information tothe user 22 regarding the size of the particular area, such as an areaof a valve or vessel, and a relative orientation of the valve or vesselto the other acquired data.

The data points 198 of the mapping data 194 can also include the timestamps, such as discussed above. The time stamps can further be used toidentify those data points acquired in a recent period, such as the datapoints 198′, which can be illustrated as darker or a different colorthan older acquired data points 198″. The illustration of a decay ortiming of the illustration of the data points can be used by the user 22to identify a most current location of the mapping catheter 100, thelead 120, or any other appropriate reason.

Surface Display

As discussed in the process 180 in FIG. 7, rendering of a surface canoccur in block 200. Rendering the surface can proceed based upontechniques, as exemplary described herein, to render a surface relativeto or with the data points 198 of the acquired data 194. Rendering thesurface can occur using at least two surface rendering techniques.

A first surface rendering technique for block 200 can include a “sweptsurfaces”. The swept surfaces rendering technique can include a sweptsurface process 240 illustrated in FIG. 9 that can render the sweptsurfaces image data 241 illustrated in FIG. 10. The swept surfacesprocess 240 can begin in a start block 242. As discussed in relation toFIG. 7, the mapping catheter 100 can be prepared and introduced in thepatient 26 as a part of the start block 242.

The swept surfaces process 240 can include selecting a sphere size inblock 244. The sphere size selected in block 244 can be any appropriatesize, such as a relative diameter of the electrode, such as theelectrode 108 or 110. According to the swept surfaces process 240, thesize of the electrode can be determined or estimated to be a sphere.Therefore, the sphere size in block 244 can substantially be thephysical size of the electrodes 108, 110 of the mapping catheter 100.For example, the sphere or radius size can be about 1 mm to about 50 mm,including about 1 mm to about 15 mm, or about 1 or 5 mm to about 15 mm.

Once a sphere size is determined in block 244, the mapping catheter 100can be moved in the patient in block 246. As the mapping catheter ismoved in the patient in block 246, the data points 198 regarding theposition of the catheter 100 can be acquired in block 248 andillustrated as the data points 198, illustrated in FIG. 10. As eachposition data point 198 is acquired, a sphere based on the sphere sizeinput in block 244 can be determined. The plurality of spheres can beused to form the swept surface rendering 241 in block 250. The displayof the surfaces of a plurality of spheres generates or renders threedimensional data regarding each of the position data points acquiredregarding the position of the mapping catheter in block 248. Therendering, however, can be limited by the size of the sphere selected inblock 244, but can be performed in substantially real time.

Because three dimensional data is displayed on the display device 58, anappropriate three dimensional surface can be displayed using the threedimensional data displayed in block 250. Moreover, the surface can beillustrated in real time allowing a real time acquisition and growth ofthe 3D surface. Accordingly, a three dimensional swept surface 241representing a passage of the mapping catheter 100 can be displayed on adisplay device 58 rather than simple individual points 198.

The swept surfaces process 240 can then end in block 252. The renderedsurface in block 200 using the swept surfaces process 240 in FIG. 9 cancreate a substantially real time surface model using the mappingcatheter 100. In addition, as illustrated in FIG. 10, the display device58 can display both of the individual points 198 of the mapping data andthe swept surfaces rendering 241 of the mapping data for viewing by theuser 22.

Again, returning reference to FIG. 7, and additional reference to FIG.11, rendering the surfaces in block 200 of the procedure 180 can also oralternatively occur with a second process including isometric or otherappropriate surface extraction procedure 280. Using the data points 198acquired and displayed on the display device 58 a surface rendering 281,illustrated in FIG. 12, can be produced with the surface extractionprocedure 280.

The surface extraction procedure 280 can begin in start block 282, whichcan include preparing and positioning the mapping catheter 100 withinthe patient 26. The data points for rendering according to the surfaceextraction procedure 280 can be acquired as discussed above, plottedrelative to the patient 26, and saved in a memory that can be accessedby the workstation 38 or any appropriate processor. Accordingly, theplotted points can be inputted into the surface extraction procedure 280at block 284. Once selected plotted points have been inputted, thesurface extraction process 280 can proceed to point discretization inblock 286. Point discretization can include appropriate hierarchies ororganizational methods, including known cube grid or octreearrangements.

If a cube grid organization method is chosen, each of the points fromthe plotted points in block 284 can be assigned to a cube of a selectedsize in a grid pattern. Each of the cubes could be assigned the datapoints that fall within the perimeter of the cube of the grid when theposition data points 198 are overlaid or aligned with the cube grid. Thecube grid could then be queried to identify those points that existwithin a selected cube. In this way, the position point data 198 can beidentified and further processed or rendered, as discussed furtherherein.

According to various embodiments, an octree procedure can also be used.The octree structure is a data organization structure that includes ahierarchal or trunk structure with nodes or leaf nodes where data pointsexist. Accordingly, a leaf node does not exist on the hierarchicalstructure unless a data point exists at the particular location.Accordingly, position data points 198 would exist on the trunk structurewhere they were determined. Thus, there is no memory wasted for emptycubes, as may exist if no data happen to be acquired for a particularcube or grid location.

According to various embodiments, point discretization in block 286allows for an indexing or layout of the data for access and furtherprocessing steps in the surface extraction process 280. Accordingly, thepoint discretization can include appropriate discretization or indexingprocesses including those discussed above. Point discretization is usedto determine an appropriate location of the data acquired and forquerying in further processing, discussed below.

After point discretization in block 286, a Gaussian Voxelization canoccur in block 288. The Gaussian Voxelization in block 288 is used tovoxelize the data into 3D data along a selected grid, such as in x, yand z directions. The voxelization of the data can include the formationof a three dimensional voxel data set along the grid pattern.

The voxelization can proceed by visiting each cube or voxel in the gridand identifying the distance of a data point that is a selected distancefrom a center of the voxel by querying the point discretization data.This can include finding all data points that are within a selectedradius from a center of each of the voxels. If a data point is found fora particular voxel, a scalar value is computed based upon the point'sdistance from the center of the voxel. A Gaussian function can be usedto determine the discretization value given to the point where the valuedecreases in the known Gaussian manner as the point deviates or isfurther from the center of the voxel. Accordingly, a data point closerto the center of the voxel is given a higher value than a point that isfurther from the center of the voxel. Each of the points within a voxelcould have different values. The value a point receives is determined byits distance from the voxel's center. So a point at the dead-center of avoxel will have a different value than a another point, which is stillin the same voxel, but deviates slightly. The value is determined by theGaussian function discussed above. A voxel with no data points can beassigned a zero. A voxel may, according to various embodiments, be givena single value even if it contains multiple points, such as the value ofthe highest valued point in the voxel.

Once the data has been voxelized in block 288, an Isometric (Iso)surface extraction can occur in block 290. The Gaussian Voxelization inblock 288 creates a substantially three dimensional volume set fromwhich a surface can be extracted in block 290. Appropriate surfaceextraction algorithms can be used to extract the surface based upon theGaussian Voxelization in block 288. For example, a marching cubesalgorithm can be used to extract a surface based upon the GaussianVoxelization data in block 288. The marching cubes algorithm can beimplemented from various sources such as the visualization tool kit athttp://public.kitware.com/vtk, incorporated herein by reference. Variousother techniques are also described in U.S. Pat. No. 4,710,876 to Clineand Lorensen, incorporated herein by reference. Other appropriateextraction techniques can also include marching tetrahedrons.Regardless, the surface extraction algorithm can use the voxelized datain block 288 to determine a surface.

Once the surface extraction is completed in block 290, the extracteddata can be saved as a geometric mesh in block 292. The geometric datacan include triangle data relating to the marching squares extractionthat occurs in block 290. The saved geometric mesh data in block 292 canthen be rendered on the display device 58 in block 294. An appropriaterendering system can be used, such as the OpenGL® rendering software orsystem (Silicon Graphics, Inc., having a place of business in MountainView, Va., USA) that defines an interface to hardware, such as thehardware of the PSU 40. The rendering of the data to the display device58 in block 294 can display the extracted three dimensional surface 281of the data acquired with the mapping catheter 100.

The extracted three dimensional surface 281 that can be viewed by theuser 22 to assist in identifying locations within the anatomy, such aswithin the heart 80, or for understanding the anatomy of the heart 80 orpositions of the mapping catheter 100 or lead 120 within the heart 80.It will be understood, that landmark icons 204 can also be displayedrelative to the extracted three dimensional surface 281, as illustratedin FIG. 12. In other words, landmarks that are identified in theposition data points 198 can be super-imposed on the extracted threedimensional surface 281 as well. It will be further understood, thatlandmarks can be illustrated on any appropriate data, such as the sweptsurfaces data 241 as well. The surface extraction process 280 can thenend in block 296. Accordingly, the surface extraction process 280 can beused to render or display a surface of the data points 198 acquired withthe mapping catheter 100.

The data points 198 acquired with the mapping catheter 100 can also bedisplayed unrendered or unfiltered on the display device 58. That is, asillustrated in FIG. 7, the mapping data can be displayed on the displaydevice 58 as the multiple points determined with the mapping catheter asa part of the position sensing unit system 40. Thus, a plurality of datapoints can be displayed on the display device for viewing by the user22.

In addition, the mapping data 194 displayed on the display device 58 canbe displayed with or without any selected filtering. For example, thedata points being displayed on the display device 58 can be displayed insubstantially real time as they are acquired and calculated. That is, asthe voltage is sensed and the impedance calculated, the determinedlocation of the mapping catheter 100 or the lead 120 can be displayed onthe display device 58.

The position sensing unit 40 can also filter the data displayed on thescreen 58. The data displayed on the screen 58 can be a smoothed oraverage location. For example, a point displayed on the screen caninclude an average location of the data points acquired and determinedfor the mapping catheter 100 or the lead 120 for a set period of time.For example, an average location of the mapping catheter 100 or the lead120 for five seconds can be displayed on the display device 58. It willbe understood, however, that a selected amount of filtering may or maynot be used to display the data points on the display device 58. It maybe selected, such as when positioning the lead electrode 126 into theheart 80, a substantially unfiltered view be given to the user 22 toallow for a substantially precise illustration of a position of the leadelectrode 126 relative to the data points or surface displayed on thedisplay device 58. This can assist in a substantially precise locationand implantation of the lead electrode 126 during a selected procedure.

Multiple Electrode Tracking

As illustrated in FIG. 12, and discussed above, data acquired with themapping catheter 100 can be illustrated on the display 58 and a surfacecan be rendered relative to the data. In addition, various otherinstruments, such as the lead 120, can be tracked or its positiondetermined with the PSU 40 and its position can also be illustrated onthe display 58 relative to the map data. In various embodiments,multiple electrodes can be positioned along the length of an instrument.For example, multiple electrodes can be positioned along the lead body120, as illustrated in FIGS. 12Ai-12Ci.

One or a plurality of electrodes can be positioned along a body of thelead 120. The lead 120 can include the implantable electrode 126 and abody of the lead 120 b can include a catheter or other portion throughwhich the lead 120 is positioned. As illustrated in FIG. 12Ai, atracking electrode 121 can be positioned relative to the implantableelectrode 120 a either directly on the body of the lead 120 or on acatheter through which lead 120 is positioned. The tracking electrode121 can be interconnected with the PSU I/O 42 via a connection, such asa wire 121 a. As discussed above, the PSU 40 can be used to identify arelative location of an electrode, such as the implantable electrode 126and the tracking electrode 121.

The tracking electrode 121, can include a ring or a band of metal, suchas a solid band of metal, that can be positioned on an insulator portionor positioned directly on the lead body 120 b or catheter through whichthe lead 120 is positioned. The tracking electrode 121 can then be usedto measure a voltage or impedance at its position on the lead 120.

If the lead 120 is positioned, such as extending through or out of acatheter, the tracking electrode 121 can be used to track a position ofa lead 120 other than the distal tip of the lead based only on theposition of the implantable electrode 126.

The tracking electrode 121 can be fixed relative to the implantableelectrode 126 along the length of the lead 120 that can be selectivelyremoved after implanting the implantable electrode 126. The trackingelectrode 121, according to various embodiments, can be fixed to thelead wall, formed integrally or as one member with the lead wall, orremovable therefrom. For example, a frangible piece could be broken bypulling on the connection wire 121 a to remove the tracking electrode121. Alternatively, the tracking electrode 121 can be provided to beimplanted with the lead 120 and not be removed.

Regardless of the connection of the tracking electrode 121 to the lead120, the display 58 can be used to display the relative position of thevarious electrodes of the lead 120. The surface data 281 can beillustrated on the display 58. A first icon element 126′ can beillustrated relative to the surface data 281. For example, the icon 126′can be used to illustrate the implanted position of the implantableelectrode 126. A second icon element 120 i′ can be used to illustrate aposition of the tracking electrode 121 positioned on the lead 120.Accordingly, the user 22, such as a surgeon can determine or be informedof a position of a selected portion of the lead 120 relative to theimplanted electrode 126.

For example, the user 22 may use the tracking electrode 121 which ispositioned at a known location on the lead 120 to determine the amountof lead slack within the patient 26. If the tracking electrode 121 ispositioned five centimeters from the implantable electrode 126, but theicons 126′ and 121′ on the display 58 are near each other, such aswithin one centimeter of each other, the user 22 can estimate the amountof lead positioned within the patient 26, such as within the heart 80.

FIG. 12Bi illustrates that the tracking electrode 121 can include aplurality of tracking electrodes 121 i, 121 ii, 121 iii and 121 iv. Eachof the tracking electrodes 121 i-121 iv can be interconnected with awire 121 a to the PSU I/O 42. Each of the tracking electrodes 121 i-121iv can be constructed substantially similarly to the tracking electrode121 illustrated in FIG. 12Ai. Accordingly, multiple positions of thelead body 120 b can be determined by tracking the multiple trackingelectrodes 121 i-121 iv. The greater the number of tracking electrodes121 the greater the resolution of the determined or illustratedgeometry. Accordingly, the number and spacing of the tracking electrodes121 can be selected for illustration and tracking resolution.

As illustrated in FIG. 12Bii, the icon element illustrating theimplantable lead 126′ and the position elements or positionlead/electrodes 121 i′-121 iv′ are illustrated. Therefore, the user 22can determine or have knowledge of a plurality of positions of theelectrode body 120 b relative to the implantable electrode 126. Again,the various positions of the electrodes can be illustrated relative tothe surface data 281 or the map data 198 on the display 58. The user 22can have knowledge of a plurality of points of the electrode body 120 bto determine a contour, length of lead within the patient 26, or otherappropriate information.

The position element or electrode 121, illustrated in FIGS. 12Ai and12Bi can be provided as a single position electrode element 123,according to various embodiments, as illustrated in FIG. 12Ci. Thesingle position electrode element 123 can include a plurality oftracking electrodes 123 i-123 iv. It will be understood that anyappropriate number of individual tracking electrodes can be provided onthe single electrode element 123 but six are exemplary illustrated. Thetracking electrode assembly 123 or the single position electrodeportions can be connected to the PSU I/O 42 with the wire 121 a. Each ofthe individual electrode portions 123 i-123 iv can be positioned on asingle flexible or rigid portion sleeve 123 a. The sleeve portion 123 acan be flexible and formed of an insulator material or of anyappropriate material to be positioned on the lead 120. Also, the severalelectrode portions 123 i-123 vi can be formed with the lead 120.

The position of the individual position electrode portions 123 i-123 ivcan be illustrated on the display 58, as discussed above. Multiple iconelements 123 i′-123 iv′ can be illustrated relative to the surface data281 or the map point data 198 to illustrate their position relative tothe surface data 281 the map points 198. The position of the pluralityof the tracking electrode portions 123 i-123 iv can be used andillustrated on the display 58 to provide information to the user 22regarding a plurality of positions of the lead body 120 b. Again, thecontour of the lead body 120 b can be used to determine the amount oflead slack or the amount of lead positioned within the patient 26 or aposition of various specific portions of the lead body 120 b.

Guidewire Tracking

In addition to tracking multiple locations on a lead or instrument, aguide wire 125 can also be tracked. As illustrated in FIG. 13A, a guidewire 125 can be positioned within the patient 26, such as relative tothe heart 80, a vein of the patient 26, or any appropriate portion. Theguide wire 125 can include a metal portion, or be substantially allmetal and be guidable within the patient 80. The guidewire can be anyappropriate guide wire, such as silverspeed™ guidewire. Generally, theguide wire 125 can include a distal end that is blunt, bent, or veryflexible to resist or reduce possibly perforating the heart 80. Theguide wire 125 can be used to assist in positioning the lead 120,including the lead electrode 126, relative to the heart 80 of thepatient. As is understood, the guide wire 125 can be used to guide alater positioned lead into the patient 26. The position of the guidewire 125, as discussed herein, can be illustrated for use by the user 22to assist in selecting an implantation site or confirming appropriatedirection of movement of the guide wire 125. For example, even when nomap is illustrated, the PSU 40 can be used to determine that the guidewire is moving generally inferiorly, superiorly, laterally, or mediallyin the patient 26.

The position of the guidewire 125, as discussed herein, can bedetermined from an insertion point. The insertion point can be a pointwhen the guidewire 125 first ends the conductive medium of the patient26, such as blood. The insertion point can be when the guidewire 125first enters the patient 26, such as insertion point 310 into a vein ofthe patient 26 or when the guidewire 125 exits another insulatingportion, such as a catheter or lead sheath. The catheter or sheath caninclude an electrode 129 that can be a position element. The lead canalso include a lead electrode 126.

Generally, the guide wire 125 and the lead electrode 126 or theelectrode 129 of the catheter or sheath can be electrically insulatedfrom one another so that each can separately and independently be usedto sense a voltage within the patient 26. The guide wire 125 can be usedto measure a voltage or determine a bioimpedance. The guide wire 125,therefore, can be connected with the PSU I/O 42. With the PSU 40 acurrent, as discussed above, can be generated within the patient 26 anda voltage can be measured with an exposed and conductive portion of theguide wire 125. The guide wire 125 can also be determined to be exposedto a conductive portion of the patient 26 by measuring an impedance in acircuit including the guidewire 125. It will be understood that theguide wire 125 can be positioned substantially independently within thepatient 26 of the lead 120 or any other portion, such as a catheter. Forexample, the guide wire 125 can be moved to a selected location withinthe patient 26, such as to position the guide wire 125 in contact aparticular apex (e.g. the right ventricular apex), and a dilator andcatheter can then be passed over the guide wire 125. The catheter can bemoved using the guide wire 125 to guide the catheter to the selectedlocation.

Once the guide wire 125 is positioned within the patient 26, and it isconnected to the PSU I/O 42 of the PSU 40, a voltage can be sensedand/or a bioimpedance can be determined at the guide wire 125. Theposition of the guide wire 125 can be determined from with the PSU 40,as discussed above including sensed voltages or determined impedances.Also, the position of the guidewire can be illustrated as a single pointor a path or surface can be illustrated to show the past path andpositions of the guide wire 125.

The measurement of the voltage or determined bioimpedance of the guidewire 125 is a single value, since the guide wire 125 is a conductor, thevoltage along it can be understood to be single value. The exposedlength of the guide wire 125 will produce a voltage value thateffectively sums the average values that would be measured at theplurality of locations which it occupies. This is because the guide wire125 can include a substantial length that is exposed, rather than arelatively small portion or member such as the lead electrode 126. Asshown in FIG. 13B, the position of the guide wire can be illustrated asan icon 125′ relative to the surface 281 or the map points 198 on thedisplay 58. If the lead 120 a is also positioned relative to the guidewire, the lead electrode 126 (shown in phantom) can be illustrated as anicon 126′ (shown in phantom) on the display 58. Alternatively, or inaddition to a lead electrode 126, the catheter with the tip electrode129 can be used and an icon 129′ can illustrate the location of the tipelectrode 129. The position of the tip electrode 129 can be determinedwith the PSU 40.

The position of the guide wire 125 can be determined according to amethod illustrated in a flowchart 300, shown in FIG. 13C. As illustratedin the flowchart 300, the guide wire position determination procedure oralgorithm can begin at start block 302. The guide wire 125 can bepositioned in the patient 26 in block 304 and an initial position orinsertion determination in block 306 can be made when the guide wire 125is first inserted into the patient 26 or exposed to a conductive medium(e.g. when exiting a catheter). The insertion position can be based onselected information. For example, the insertion position can be basedon an initial measurement or determination taken when only a selectedlength of the guide wire 125 is positioned in the patient in block 306a. For example, it can be selected to position the guide wire 125 alength into the patient 26 such that a measured bioimpedance issubstantially equivalent to a point or single location. Alternatively,the insertion location of the guidewire can be a distal end of thecatheter 120 which has an electrode 129 or position element at thedistal end. The measurement with the electrode at the distal end can beused as the insertion point determination in block 306 b and illustratedas icon 129′ on the display 58. Also, the guide wire may extend from anyappropriate portion such as the lead and may extend past the leadelectrode 126. The lead electrode, if insulated from the guidewire 125,can used similar to an electrode on a distal end of the catheter 120.Also, the insertion position can be manually input in block 306 c.

Based on the insertion position in block 306, as illustrated in FIG.13B, the surface 281 can be generated to illustrate a surface of aselected portion of the patient 26. It will be understood, however, thatthe position of the guide wire 125 need not be illustrated relative tothe surface 281 or the map points 198 but can be illustrated as arelative location on the display 58. Regardless, the insertion point ofthe guide wire 125 can be an insertion point 310 illustrated in FIG.13A. This insertion point 310 can be any appropriate point in thepatient 26 for positioning the guide wire 125 within the patient forperforming a procedure. The insertion point can also be a point wherethe guide wire 125 first extends from an insulated sheath, such as thecatheter 120 or past the lead electrode 126. Regardless, the insertionpoint determined in block 308 can be used to illustrate the position ofthe guide wire 125 within the patient when a selected or substantiallength of the guide wire is exposed within the patient 26.

The guide wire can then be advanced in block 312. A measurement of thebioimpedance on the guide wire can be made at any selected point orsubstantially continuously in block 314. The measured bioimpedance alongthe guide wire in block 314 can be measured in any appropriate matter,similar to the manner of measuring the bioimpedance of any appropriateelectrode as discussed above. For the guide wire 125, however, thedetermined bioimpedance can be understood to be an average or cumulativemeasurement along the length of the exposed wire in block 316. In otherwords, the voltage sensed or the impedance determined is a single value,but is based on the entire length of the guide wire 125 that is exposed.Thus, the single value of the guide wire 125 is determined to be at amidpoint of the exposed portion of the guide wire 125. As discussedabove, the determined bioimpedance at any electrode can be used toillustrate a relative position of the electrode on the display 58.Accordingly, the measured impedance at the guide wire in block 314 canbe used to determine a single position in block 318.

The reported position of a guide wire 125 is simply a point that isrelated to the single value (average) of the measured impedance and isgenerally the midpoint of the guide wire 125. The position of the distalend of the guide wire 125, however, can be determined in block 320 andis based on the known insertion point form block 308. The position ofthe distal portion of the guide wire 125 can be determined, andrepresented on the display device 58, as a point that extends from theinsertion point (e.g. where it exits the lead or catheter) to twice thelength from the insertion point, determined in block 308, and thedetermined position in block 318. Accordingly, a projection of thelength of the guide wire 125 that is twice the distance from theinsertion point determined in block 308 and the determined position ofthe guide wire 125 based on the determined bioimpedance in block 318 canbe performed in block 320.

The position of the guide wire 125 can be illustrated on the display 58,as illustrated in FIG. 13B, as a single point 125′ that isrepresentative of a position of the distal end of the guide wire 125.Alternatively, or in addition thereto, the guide wire 125 can beillustrated as an icon 125 a′ that extends from the insertion positionto the point that is twice the length of the distance from the insertionposition to the determined position in block 318. Also, multiple pointscan be displayed to show a surface or a trail of points showing adetermined path of the guide wire 125. It will be understood, however,that the represented position of the distal end of the guide wire 125may have a certain error if the guide wire 125 physically bends withinthe patient 26.

Once the length of the guide wire is projected or the position of thedistal tip is determined, it can be projected or displayed on thedisplay 58. It will be understood that the displayed position of theguide wire 125 can be updated substantially continuously or sequentiallyas selected by the user 26. After the projection of the guide wire 125in block 320, a decision of whether the guide wire will be furtheradvanced can be made in block 322.

If it is determined that the guide wire 125 should be further advanced,then the YES routine 324 can be followed to advance guide wire 125,further in block 312. If it is determined that the guide wire 125 is ata selected or appropriate location, such as for guiding the lead 120 toa selection location within the patient 26, the NO routine 326 can befollowed to an end block 328. It will be understood that the end block328 can simply illustrate an end for determining a position of the guidewire 125 and not an end of a complete surgical procedure. For example,as discussed above, the guide wire 125 can be used to guide the lead 120to a selected position within the patient 26. Accordingly, once it isdetermined that the No routine 326 should be followed to end the guidewire advancement procedure that the lead 120 can be advanced over theguide wire 125 to its selected location.

Clarifying a Three Dimensional Nature of Data

The display 58 can be a two dimensional display that is displaying themap data in a three-dimensional manner. As illustrated in FIG. 15A and15B, however, the virtual view of the data can be changed to moreclearly and/or distinctly represent the three-dimensional (3D nature) ofthe map data. Rocking or rotating a view of the map data can clarify orenhance an understanding of the 3D nature of the map data on the display58.

As illustrated above, for example in FIGS. 6 and 12, an image of mapdata can be displayed on the display 58 that represents the anatomy ofthe patient 26. The display 58, however, can include a video monitor,such as a CRT or LCD display, that is substantially two dimensional. Asfurther discussed above, the mapping data generated regarding thepatient 26 can be substantially three dimensional. As illustrated inFIG. 2, three axis, x, y, and z, can be generated relative to thepatient 26 through the use of the various electrode patches 46 a-50 b.

As illustrated in FIG. 6, the data, for example, the map points 198, canbe displayed from various perspectives. An anterior-to-posterior andmedial-to-lateral perspective or oblique perspective can be viewed onthe display 58. The views on the display 58, however, can besubstantially static. Although one skilled in the art will understandthat the static images represent a single view of the patient 26, basedon the data that is mapped of the patient 26, various three dimensionalfeatures that have been mapped may remain substantially hidden in abackground because of the three dimensional nature of the data beingdisplayed on a two dimensional surface of the display device 58.Accordingly, a rocking or vibrating method can be used to illustrate animage on the display device 58 that is substantially not static or atleast a view of the image where the data is not static. A virtual cameracan be provided to move relative to the plotted or displayed map datapoints 198 or the surface 281 to allow the user 22 to more clearlyunderstand the three dimensional nature of the data.

As illustrated in FIG. 14, a method 370 illustrated in a flowchart canbe used to illustrate a three dimensional nature of a data, such as themapping data acquired of the patient 26, on a substantially twodimensional display. As further illustrated in FIGS. 15A-15B, a rotatingvirtual camera (VC) can be used to generate or display a changing twodimensional view of a three dimensional object, whether real or virtual.The image on the display 58 is from the viewpoint of the virtual cameraVC. According to the method 370 in FIG. 14, the rocking procedure canbegin in block 372. After starting the method 370, display of the mappeddata, including either or both of the points or surfaces, can be done inblock 374, as illustrated in FIG. 15A. Discussion herein to FIGS. 15Aand 15B of a “T” is merely for clarity. The user 22 can then make adecision on whether to turn rocking ON or OFF in block 376. If the userturns OFF or does not start rocking, the OFF routine can be followed tothe stop block in block 378. If the user turns ON the rocking, then theON routine can be followed to select a focal point relative to thedisplayed map data in block 378.

When selecting a focal point F in block 378, illustrated in FIG. 15A,the focal point can be selected substantially automatically by analgorithm, manually by the user 22, or in a combination thereof. Forexample, the focal point can be selected by the algorithm as asubstantially geometrical center of the mapped data displayed in block374. Alternatively, the user 22 can identify an area or point within thedisplayed map data or at a position relative to the displayed map datafor selection as the focal point. Accordingly, the focal point need notbe within a boundary of the map data.

Once a focal point is selected in block 378, a circle or arc, asillustrated in FIG. 15A can be defined around a y-axis, generated ordefined relative to the map data displayed in block 374, or a center atthe focal point selected in block 378. A radius R, as illustrated inFIG. 15A, can also be defined based upon a current location of thecamera or at any selected radius in block 380. It can be selected, forexample if the rocking is not to interfere or be substantially seamlesswith viewing of the map data, that the radius of the circle defined inblock 380 be equal to the distance defined from the focal point to thecurrent view point of the virtual camera for viewing the map data. Itwill be understood, however, that the radius can be predefined by theuser or automatically by the system and the virtual camera can be movedto that radius.

After the circle is defined, including the radius in block 380, the arcof the circle in which the camera is to travel can be defined in block382. Again, it will be understood, that the arc for moving the camera inblock 382 can be defined manually by the user 22, by a system, such asthe PSU 40, or in a combination thereof. For example, the PSU 40 caninclude a preset arc of movement such as about 15 degrees. The user 22can augment the arc of movement, however, either before or after viewinga set number of repetitions of rocking to an arc greater or less than apreset amount. Additionally, or alternately thereto, if the user selectsto turn ON the rocking in block 376, an initial pop-up or configurationmenu can be provided and the user can select various features, such asthe radius in block 380, the arc in block 382, and various otherfeatures as discussed herein.

For example, the direction for movement of the VC along the arc can beset in block 384. Again, the direction for movement along the arc can beuser selected, system selected, or a combination thereof. The directionfor rocking can also be selected prior to illustrating any rocking,after a set number of repetitions of rocking, or at any appropriatetime. Generally, however, the camera is able to rotate or move along thearc in a clockwise or counter clockwise direction which can be selectedor started in block 384.

The VC can be moved for one time step or increment along the arc definedin block 382 defined in block 386, as illustrated in FIG. 15B. The VCwill move in the direction set in block 384. The time step can include adistance of travel, such as a set number of degrees, per cameramovement. For example, the system or user 22 can select to move thecamera one degree, two degrees, three degrees, or any appropriate numberof degrees. For example, if the arc is defined as 15 degrees in block382, and the user 22 wishes to view five views of the data, then a timestep can be defined as three degrees. Accordingly, the camera can bemoved three degrees per time step and one time step can be traveled inblock 386.

The map data can then be redisplayed in block 388 based upon theposition of the camera in block 386. As discussed above, the map data,including the map data points 198 or the surface 281, is data or pointsgenerated by measuring a portion of the patient, such as the heart 80.Accordingly, if the data does not move, but a perspective of viewing thedata moves, then the view of the data may be altered. For example, asillustrated in FIG. 6, anterior-to-posterior and oblique views can beprovided to illustrate the data from a different perspectives to showvarious anatomical features. A further example is illustrated in FIGS.15A-15B.

After the points are re-displayed in block 388, the user 22 candetermine whether rocking should be stopped in block 390. As discussedabove, the query for stopping rocking can occur at any time such asafter a set number of repetitions of rocking, a set number of timesteps, or at any appropriate time. Therefore, manual input from the user22 may or may not be necessary to follow the YES routine to the stopblock 378. Similarly, manual input from the user 22 may or may not benecessary to follow the NO routine to the decision block 392 of whetherthe camera has reached the end of the arc.

As discussed above, the length or extent of the arc can be identified ordetermined in block 382. If it is determined that the VC has not reachedthe end of the arc, then the no routine can be followed to move the VCone more time step in block 386. At that point, such as at a second timestep from the initial position (i.e., i+2) of the VC, the data pointscan be redisplayed in block 388 and the user can again be queried as towhether the rocking should be stopped in block 390.

Returning reference to the decision block of whether the camera hasreached the end of the arc in block 392, the YES routine can be followedto switch direction of travel in block 394. If switching the directionof travel is determined in block 394, the camera can move one time stepalong the arc in the current direction of travel in block 386, which canbe the reverse of the initial direction selected in block 384. This canallow the rocking motion, as the VC can move along the arc in selectedtime steps and then seamlessly reverse direction. At each time step, thepoints can be redisplayed in block 388.

As illustrated in the flowchart 370, a rocking of the viewing of the mapdata can be performed substantially automatically after defining a focalpoint and moving a VC relative to the data. Returning reference to FIG.15A and 15B a three dimensional object 400 is illustrated in FIG. 15A.The three dimensional object 400 can be any appropriate object and isillustrated as a “T” for simplicity of the current discussion. A focalpoint F can be identified, as in block 378. The vertical or y-axis canalso be identified relative to the data. A virtual camera (VC) can bedetermined or positioned at some radius (R) along the x-axis. An arc acan also be defined, as in block 380. As discussed above, a directionand the time step of the VC can then be identified in blocks 384 and 386and the VC can move.

As illustrated in FIG. 15B, once the VC has moved a first time step,(i+1), the perspective of the virtual camera has changed relative to thethree dimensional data 400 from the initial position “I” of the VC. Adifferent perspective can show hidden data or data not viewable from thefirst perspective at position (i) on the arc a. For example, an open orhollow area 402 is clearly seen from the second perspective at the firsttime step (i+1) that can not be seen due to the surface data 404 at thefirst perspective at the first point (i).

The VC can continue to move along the arc as discussed in the flowchart370. Once the VC reaches a final point (f), which can be two time steps(i.e., i+2), the virtual camera (VC) can switch directions, such as inblock 394, or be stopped such as in the user 22 stopping the rocking inblock 390. Regardless, the changed perspective relative to the data 400can allow the user 22 to more clearly understand the data 400 in itsthree dimensional nature even though the display is a substantially twodimensional display, such as the display 58. The rocking can enhance theuser's perception of the spatial relationships of the data displayed onthe display device.

Implantable Device

As discussed above, the PSU 40 can be used to implant any appropriatesystem, for example an implantable medical device (IMD) 600 can beimplanted, shown in FIG. 16. The IMD 600 and its associated lead orleads 120 can be implanted without the external imaging device 28.Although, it will be understood, that the imaging device 28, orappropriate imaging device, can be used during an implantationprocedure, such as to confirm placement of the lead 120 once positionedwith the PSU 40. It will also be understood, that the PSU 40 can be usedto supplement placement of an implantable member, such as the lead 120,with the imaging device 28, to reduce the number of images acquired, oreliminate direct imaging of the patient 26 and instruments entirely.

The IMD 600 can include implantable pacemakers, implantable cardioverterdefibrillator (ICD) devices, cardiac resynchronization therapydefibrillator devices, or combinations thereof, exemplarily illustrated.An exemplary dual chamber IMD can include the Concerto Model C154DWK,sold by Medtronic, Inc. of Minneapolis, Minn., USA, but appropriatesingle chamber IMDs can also be implanted. The IMD 600 can include animplantable case or body assembly 602. The implantable case 602 can beformed of appropriate materials and include appropriate features, suchas a hermetically sealed body wall. The body wall can be made of asubstantially inert material or of a conducting material.

The lead assembly 120 can be interconnected with the implantable case602 at a selected time. As discussed above, the lead can be guided to animplant location, such as in a right ventricle, with the PSU 40. Thelead 120 can then have its electrode 126 fixed to the heart 80. It willbe understood, however, that any appropriate number of leads can beinterconnected with the implantable case 602 and can include anyappropriate number of electrodes.

The PSU 40 and the various methods discussed above can be used toimplant the lead 120 and other portions, such as an implantable medicaldevice. The implantable medical device can be programmed once it isimplanted, as illustrated in FIG. 16. A programmer or programming system610 can be provided to program the implantable medical device. Theprogrammer 610 can include a telemetry system that is operable towirelessly transmit a signal to the processor within the case body 602.It will be understood that a wired communication system can also beused. In addition, an induction system can be used where a coil ispositioned near the case body 602 and a signal is sent from theprogrammer via induction. The programmer 610 can also receiveinformation from the IMD 600 (e.g. time and duration of arrhythmias andprogramming settings) to assist in providing an appropriate program forpacing. The programmer 610 can include any appropriate programmingsystem, including one generally known to those skilled in the art, suchas the Medtronic 2090 or Carelink™ programmer, provided by Medtronic,Inc. of Minneapolis, Minn., USA.

Distortion Correction

The map data, or the illustration thereof, may be distorted because ofvarious effects. Correction for the distortion, as discussed herein andillustrated in FIGS. 17-19B, can assist in displaying the map datapoints and determining a position for implanting leads or the IMD 600.As discussed above, map data can be generated and used to illustrate mapdata points 198 or a surface 281 on a display 58. The lead 120 can thenbe tracked or guided with the PSU 40 or any appropriate tracking systemrelative to the patient 26. To appropriately collect and illustrate thedata on the display 58, however, various corrections can be made to thedata or calibrations to the system 40 to ensure correct and plausibleillustration of the data on the display 58. According to variousembodiments, a calibration or correction can be performed to correct fordistortions that may be realized or encountered within the patient 26when using the PSU 40. As illustrated in FIG. 17, a flowchart 650illustrates a method 650 for correction of various inherent orencountered distortions within the patient 26.

With continuing reference to FIG. 17, the method 650 illustrated in theflowchart can begin in start block 652. An instrument, such as themapping catheter 100 including the tip 108 and ring 110, can then bepositioned in the patient in block 654. It will be understood that thediscussion of a tip and ring herein is merely a specific example of aninstrument that can include two or more electrodes that are positioned arelatively fixed distance to one another. As an example, as illustratedabove, the mapping catheter 100 can include the tip electrode 108positioned on the distal end of the instrument and a ring electrode,such as the ring electrode 110 positioned proximally of the balloon 102portion of the mapping catheter 100. Accordingly, the tip and ringdiscussed in the flowchart 650 can exemplary be the tip and ringelectrode illustrated in the mapping electrode 100. It will beunderstood, however, that the tip and ring may simply be any twoelectrodes on an instrument. For example, the tip and ring can be adistal and proximal electrode that are positioned at a substantiallyfixed location relative to one another of any instrument. For example, abipolar pacing lead can be positioned relative to the heart 80 formapping or for implantation. Using the calibration or correction of theflowchart 650 can also be used to calibrate or correct the position ofthe two electrodes of a bipolar lead.

Once the instrument with a tip and ring electrodes are positioned in thepatient in block 654, electrode impedance data can be collected for thetip and ring electrodes in block 656. As discussed above, the PSU 40 caninclude the electrode patches 46 a-50 b that can inject currents intothe patient 26. The currents cause a voltage change or current to beformed between pairs of the electrodes and an impedance can be measuredwithin the patient 26. Accordingly, as discussed above, impedances canbe measured with the electrodes and a relative position of theelectrodes can be determined.

A position of the tip and ring can be determined in block 658. Thecollection of the electrode impedance data in block 656 can be used todetermine the position in block 658. The collection of the tip and ringelectrode impedance data in block 656 for determining the position inblock 658, can be performed substantially immediately after both the tipand ring electrodes are within the patient 26. Accordingly, positioningthe tip and ring instrument in the patient 26 in block 654 can simply bepositioning the tip and ring electrodes within the patient 26 so thatthey can be used to measure an initial or first impedance within thepatient 26.

A vector can be calculated from the ring to the tip based upon thedetermined position of both the tip and ring electrodes in block 660. Asdiscussed above, the ring electrode can simply be an electrode that isproximal to the tip electrode. Accordingly, the vector can be understoodto be a vector that is defined from a proximal electrode through adistal electrode. Additionally, as discussed above, determining theposition of the tip and ring can be performed substantially immediatelyafter placing the tip and ring electrodes within the patient 26. Thus,the initial measurement can be a standard or undistorted measurement ofthe relative position of the tip and ring.

Also, the first measurement may include a plurality of firstmeasurements. For example, a first measurement in each of the axis thatare generated within the patient can be made. Thus, calibration or errorcorrection can be made for each of the axis. Moreover, the calibrationcan be performed once the mapping catheter 100 is positioned within theheart 80. Accordingly, identifying the portion of the heart 80 for alocation of the mapping catheter 100 can be used to assist incalibration of the PSU 40.

As discussed herein, the flowchart 650 illustrates a method ofcorrection or accounting for distortion in a current or sensed impedancewithin the patient 26. Accordingly, the correction using the flowchart650 can be used to ensure that all or substantially all of the impedancemeasurements collected within the patient 26 used to plot map datapoints 198 are positioned at a known or similar position relative to oneanother. In other words, using a standard or calibrated distance of thetip from the ring allows distortion of the determined or measureddistances between the two to be reduced or eliminated.

After a vector is calculated based upon a determined position of the tipand ring electrodes in block 660, a distance can be selected from thering electrode in block 662. The distance from the ring electrode can bethe measured distance from the ring electrode to the tip electrode, alsobased upon the determined position of the tip and ring electrodes inblock 658. Alternatively, any appropriate distance can be selected forthe tip electrode from the ring electrode. For example, it may beselected to determine a distance that is slightly less than the physicaldistance of the tip electrode from the ring electrode to ensure that thetip electrode is touching or imbedded a selected distance into aphysical surface when displaying the tip electrode is at or on asurface. Alternatively, it can be selected to determine a distance inblock 662 that is greater than the physical position of the tipelectrode from the ring electrode. This ensures that there is a spacebetween the tip electrode and any surface when it is displayed that thetip is at a mapped surface. For example, if a surface is determined withthe mapping catheter 100 and the lead 120 is to be implanted, it can beselected to navigate the lead 120 to an implanted location with theillustrated map data, but while attempting to maintain a distancebetween the lead 120 and any surface of the patient 26 prior toimplantation of the lead 120 into the patient.

Once the vector is calculated in block 660 and a distance from the ringelectrode is determined in block 662, a plotted position of the ring canbe performed in block 664. Additionally, a point along the vectorcalculated in block 660 and at the distance selected in block 662 can beplotted in block 666. After plotting the position of the ring electrodeand plotting the position of the second point in blocks 664, 666respectively, two points can be plotted that represent a position of thering electrode and the tip electrode. As discussed above, a measurementof an impedance of the ring and tip electrodes can be performed in block656. Accordingly, the PSU 40, which the tip and ring instrument can be apart of, can determine a position of the ring electrode based upon themeasured impedance. The measurement of the impedance at the ringelectrode can be used to plot the position of the ring electrode basedupon its determined position in block 658. However, to correct forvarious distortions, calculating or selecting a distance of the ringelectrode from the tip electrode in block 662, can ensure that allmeasurements or plotting of the tip electrode are the same. In otherwords, rather than determining two positions individually for eachelectrode, only one is determined by measurements. Thus, distortion canbe reduced or eliminated for the display of two points if the second isalways a fixed distance from the first. Also, the determination ofposition can be made for only one electrode and the position ororientation of the second as only a direction from the first.

Decision block 668 is used to determine whether more data are to becollected. If the YES routine 670 is followed, then measurements ofimpedance at the tip and ring electrodes can be performed in block 656.A second decision block can be used to determine whether the measurementin block 656 was a first measurement in block 672. If the YES routine isfollowed in 674, then a determined position of the tip and ring,calculated vector in block 660, and selected distance can be performedin block 662. If the NO routine is followed in 676, for example, if avector has already been calculated in block 660 and distance has alreadybeen selected in block 662, a position of the ring electrode can bedetermined in block 678 based upon the subsequent measurement. Aposition of the ring can then be plotted in block 664 based upon thedetermined position in block 668. Further, a position of the secondpoint can be plotted in block 666 based upon the calculated vector andselected distance in blocks 660, 662.

If no further data is collected in block 668, then the NO routine 660can be followed to optionally render the map data points 198 or thesurface 281 in block 682 or to end the procedure in block 684. It willbe understood, that rendering a surface in block 662 is optional, atleast because the correction method in the flowchart 650 can simply be acalibration procedure.

To graphically illustrate the differences between collecting data withan uncorrected and with a corrected tipping ring or dual electrodeposition, FIGS. 18A and 18B illustrate icons representing a dualelectrode or tip and ring instrument in an uncorrected and correcteddisplay, respectively. FIGS. 19A and 19B also illustrate a plurality ofmap data points illustrated on the display 58, also in both anuncorrected and corrected manner, respectively. Briefly, withoutcorrection, the data in FIGS. 18A and 19A is more spread out anddistorted than in corrected FIGS. 18B and 19B.

With additional reference to FIG. 18A, an icon 100′ can be illustratedon the display 58. The icon 100′ can include a first icon portionillustrating the determined or measured position uncorrected of the ringelectrode 110 uC. The display 58 can further include an icon portionillustrating a position of the tip electrode 108 as an icon 108 uC. Theuncorrected positions of the ring and tip electrodes 110 uC, 108UC, canbe determined to be a position or distance D_(UC) apart. The distanceD_(UC) can be a determined distance based only upon the measureddistance or measured impedance at the two electrodes, such as the ringand tip electrodes, 110, 108 of the mapping catheter 100.

As illustrated in FIG. 18B, however, the display 58 can display an iconof the mapping catheter 100 relative to map data points 198 and furtherinclude a first icon portion representing a corrected position of thering electrode 110 c and a second icon portion representing a correctedlocation of the tip electrode 108 c. The distance between the correctedring electrodes D_(c) can be less than, greater than, or any correcteddistance relative to the uncorrected distance D_(uc). As discussedabove, during an initial or first placement of the mapping catheter 100within the patient 26, a distance can be selected of the tip electrodefrom the ring electrode. The distance selected can be used to illustratethe corrected position of the icon 108 c relative to the ring electrode110 c icon. The corrected distance can be a calibrated distance that isto maintain the selected or measured distance on the display 58 for allpoints that are measured within the ring electrode when illustrating thetip electrode relative thereto.

As illustrated in FIG. 19A, when the map data points 198 are displayedon the display device 58, uncorrected map data points 198 uc may beexpanded where a distance may be present between various map data pointssuch as in regions 198 uc′ and 198 uc″ compared to corrected orcalibrated map data points 198 c illustrated in FIG. 19B. A more compactregion of the map data points can be seen in regions 198 c′ and region198 c″ in FIG. 19B, The region 198 uc′ compared to the region 198 c′illustrates that the corrected data illustrates more compact map datapoints in the corrected map data 198 c. The compact data and thecorrected map data point 198 c are based upon the substantially knownand unchanging position of the ring electrode relative to a distal tipof the instrument, which can include the tip electrode 108. Within thepatient 26, however, the measured impedance may be altered due tolateral (or distorted) electrical current flow within the patient, softtissue within the patient, or other distortion causing features of thepatient 26. Although the measured distance of the tip electrode relativeto the ring electrode may differ based upon the distortions, thephysical position of the tip electrode relative to the ring electrodecan be substantially fixed based upon the physical properties of themapping catheter. Accordingly, accounting for the physical properties ofthe mapping catheter, a single measure of points, such as a measuredpoint of the ring electrode, can be used to map at least two pointsrelative to the ring electrode. Also, the ring electrode is less likelyto extend to or near a chest or thorax wall and, therefore, is lesslikely to be close to the outside of the body and therefore, more likelyto measure an accurate position than a tip electrode.

It will be understood that although the method illustrated in theflowchart 650 is discussed to determine a position of a distal tipelectrode relative to a more proximal electrode that the alternative orreverse may also be performed. For example, a corrected or calibratedposition of a proximal electrode can be determined relative to a distalelectrode by determining a vector from the distal electrode towards theproximal electrode and selecting a distance between the two.Accordingly, measuring from the ring electrode or any proximal electrodeis not necessary.

In addition, it will be understood, that the PSU 40 can allow the userto select display types or simultaneously view both corrected anduncorrected map data points. Therefore both corrected and uncorrectedmap data points can be displayed on the display 58. They can bedisplayed sequentially on a same area of the display or next to eachother on the display 58 for view by the user 22. In addition, it will beunderstood that the map data points 198 can be illustrated alone, asillustrated in FIGS. 19A and 19B, or a surface can be rendered anddisplayed without the map data points 198. The rendered surface can begenerated or based upon the corrected or uncorrected data points and acorrected or uncorrected surface can also be displayed on the display 58similar to the map data points 198.

According to various embodiments, the correction for the position ordistance between two or more measuring electrodes within the patient caninclude a scaling factor that can be used to correct the map of data.This can be an alternative to or in addition to the method 650illustrated in FIG. 17. The scaling factor can be determined based uponpoints identified or determined of the two electrodes positionedrelative to one another. The two electrodes, such as on the mappedcatheter 100, can be substantially fixed relative to one another for thecorrection procedures. The position of the two electrodes can becollected continuously during a procedure or at any appropriate time.The scaling factor can be used to correct the map, such as the map datapoints 198 or the surface 281.

With Reference to FIG. 20, a method of formulating a scaling factor andinterpolating the map data 194 is illustrated in the scaling factorinterpolation (SFI) flow chart 421. In the SFI flowchart 421, the methodcan begin in Start block 423. The volume or surface to be mapped canthen be explored and mapped in an acquire map data or points block 425.

As previously discussed, the mapping catheter 100 can include two ormore electrodes, such as the tip and ring electrodes 108, 100 (althoughany instrument can include any appropriate number of electrodes, andonly two electrodes are discussed for simplicity of the presentdiscussion). Each of the electrodes can be used to measure impedancewithin the volume, such as within the heart 80 of the patient 21. Duringeach cycle of acquisition, the PSU 40 can also determine the measureddistance between the two electrodes 108, 110. The distance between thetwo electrodes 108, 110 can be known based upon an input orpredetermined distance. The known distance can be recalled in block 427from a memory or input system.

The measured distance can be compared to the known or input distance.The comparison can be used to determine a scaling factor in block 429.Because the map data can be three dimensional, a scaling factor in eachof three coordinates, x, y, and z can be determined. The scaling factorcan be determined for one or any appropriate number “n” of points. Thus,scaling factors r_(nx), r_(ny), and r_(nz) can be determined for npoints of map data 194.

The scaling factors r_(nx), r_(ny), and r_(nz) can all be determinedbased on the initial of determined scaling factor based on a distancebetween at least two electrodes or position elements on the instrument,such as the electrodes 108, 110 on the mapping catheter. The twoelectrodes 108, 110 will be at relative positions to one another inthree dimensions. Accordingly, the scalar distance can be calculatedbased on the known orientation between the two electrodes 108, 110 andapplied to the map data in the three dimensions.

The scalar distance can be used to determine a vector based on ameasured or determined orientation of the two electrodes 108, 110relative to one another when collecting the map data. A correctionvector based on the scalar distance and a determined three dimensionalposition of the tip electrode 108 and the ring electrode 110. Thecorrection vector, using the scalar value or distance, can then be usedto determine a scalar value in all three dimensions to determined orgenerate the scaling factors r_(nx), r_(ny), and r_(nz).

Using the scaling factors r_(nx), r_(ny), and r_(nz) the measured orsensed positions of the electrodes 108, 110 that generate the map datapoints 194 can then be corrected to generate an interpolated map data inblock 431. The interpolated data can be similar or identical to that inFIG. 19B, which is corrected data. The uninterpolated data can besimilar or identical to the uncorrected data in FIG. 19A. As illustratedabove, in FIGS. 19A and 19B, the difference between the interpolated andun-interpolated data can be significant if distortions exist in thevarious currents used to generate the map data points. The interpolationcan be performed with any appropriate algorithm, such as the griddata3function of Matlab® computer software, sold by MathWorks Inc. Theinterpolation can correct each measured map data point to a corrected orinterpolated map data point.

In essence, the scaling factor is a difference, such as a mathematicalratio, between the determined position in the acquired map data pointsof the electrodes and the known position of the electrodes. If the mapdata points determine that the two electrodes are 3 cm apart, but it isknown that they are 2 cm apart then the scaling factor serves tonormalize the measured data. Further, because the data can be collectedin three spatial dimensions the scaling factor can be determined andapplied in all three spatial dimensions.

The interpolated map data can be displayed on the display 58 in block433. As illustrated in FIG. 19B, the interpolated or corrected map datacan correct for distortions. Further, the map data can be displayed aspoints 198 and/or the surface 281. The interpolated map data can then beused for navigation or guidance, if selected, in block 435. It is notrequired, however, that the interpolated data, or any data, be used fornavigation. The method can then end on block 437.

Virtual Map Data

The map data, whether corrected or not, can be collected solely bymeasuring impedances with electrodes, such as with the mapping catheter100. Map data, however, can also be determined by knowing the dimensionsor surface of a physical structure relative to the electrodes measuringimpedance or other tracking members. As illustrated in FIGS. 21A-21C,virtual map data points can be collected or determined relative to themapping catheter 100. The map data can be collected based on knowing ordetermining relative locations of an instrument used to collect the mapdata points. Thus, the map data points or the surface, illustrated forviewing by the user 22, according to various embodiments can begenerated and displayed without requiring information from anotherimaging system, such as a fluoroscope, MRI, etc.

The map data points 198 illustrated on the screen or display 58 can bepoints that are generated based upon a sensed or measured impedancewithin the patient 26, as discussed above. In addition, the data that isillustrated as the map data points 198 is based upon map data 194collected with the PSU 40. As illustrated in FIG. 21 a, the map point194 can be based upon an actual measurement of a voltage or bioimpedanceat selected locations within the patient 26. For example, the impedancemeasured at the tip electrode 108 and the ring electrode 110 can be usedto determine a position of the specific location or relative location ofthe tip and ring electrodes 108, 110.

In addition to the actual positions of the tip and ring electrodes 110,108 that are measured with the mapping catheter 100, various positionsthat are known locations relative to the ring and tip electrode can alsobe inferred by the PSU 40. The PSU 40, as discussed above, can include aprocessor that is interconnected with a memory system that can storeexecutable instructions for various calculations. Calculations caninclude the determination of relative or inferred or determinedpositions of various physical portions of the mapping catheter 100relative to the two electrodes of the tip and ring, 108, 110.

Exemplary inferred positions can include points on or a complete surfaceof a physical structure of the mapping instrument or catheter 100. Asdiscussed above, the mapping catheter 100 can include the balloon 102that is inflated between the tip and ring electrodes. The balloon caninclude a known physical dimension, such as a diameter that can be usedto infer or determine one or more points or a surface along a spherebetween the tip and ring electrodes 108, 110. These points or surface,also referred to as virtual points or surface, can be inferred ordetermined based upon the measured impedances of the tip and ringelectrodes 108, 110. The virtual surface can be defined by a pluralityof virtual points defined on the physical surface of the mappinginstrument.

As illustrated in FIG. 21A, if and when only the measured impedances ofthe tip and ring electrodes 108, 110 are used to determine map points194 there are only two points that can be measured per time step ormeasurement instant. Points 108 p and 110 p can correspond to the twopoints of the measured impedance with the tip electrode 108 and the ringelectrode 110, respectively. These points can be displayed on thedisplay 58 as map data points 198 and can be used to accumulate aplurality of points for illustrating the surface 281. Because theballoon 102 is positioned at a fixed location between the tip and ringelectrodes 108, 110, and if inflated sufficiently so when in blood, doesnot noticeably compress, the surface of the balloon 102 can also be usedto identify known points relative to the tip and ring electrodes 108,110.

Determining points on the surface of the balloon 102 uses the knowngeometry of the balloon 102 relative to the tip electrode 108 and thering electrode 110. Once the balloon 102 is inflated, it can besubstantially rigid and at a fixed location between the tip and ringelectrodes 108, 110. This allows the surface of the balloon 102 to bedefined relative to the tip and ring electrodes 108, 110. For example, acenter of the balloon can be identified as 102 c and as a point along aline between the tip and ring electrodes 108, 110. The geometry of theballoon relative to its center 102 c can be any appropriate geometry.For example, the balloon 102 can be substantially a perfect sphere.Accordingly, the surface of the sphere can be determined relative to thecenter 102 c. Alternatively, as illustrated in FIG. 21B, the balloon 102can have an ovoid shape. Regardless, the surface of the balloon 102 canbe determined relative to its center 102 c and the two electrodes at thetip and ring 108, 110 of the mapping catheter 100.

Once the surface of the balloon 102 is determined relative to the tipand ring electrodes 108, 110, the surface of the balloon 102 can be usedto generate map data 194 in addition to the two points based only uponthe measured impedance of the tip and ring electrodes 108, 110. Forexample, at each time increment where an impedance measurement is takenfrom the tip and ring electrodes 108, 110, a determination of one ormore points defined by a surface of the balloon 102 can be determined.For example, as illustrated in FIG. 21B, surface point's 102 p 1-102 p 6can be determined. As illustrated in FIG. 21C, it will be understoodthat the balloon 102 is a substantially three dimensional object.Accordingly, points around the surface can be determined, which caninclude a point 102 p 7 that can be across or substantially opposite thepoint 102 p 2 and rotationally offset from other points 102 p 1 and 102p 3 by 90 degrees or about 90 degrees.

The determined points of the surface of the balloon 102 need not bespecifically measured or be based upon a measurement of an impedancewithin the patient 26. Rather, the points on the surface of the balloon102 can be determined as specific location relative to the locations ofthe tip and ring electrodes 108, 110 based upon the impedancemeasurements at the tip and ring electrodes 108, 110. Accordingly, eachtime a measurement is taken of an impedance with the tip and ringelectrodes 108, 110 and positions of the ring and tip electrodes 110,108 are determined based upon the impendence measurements, a number ofpoints defined by a surface of the balloon 102 can also be determined.The points defined by the balloon 102 can be determined by calculatingthe geometry of the points of the balloon 102 relative to the tip andring electrodes 108, 110. Each of the points determined relative to theballoon 102, based upon the geometry of the balloon 102 relative to thetip and ring electrodes 108, 110, can also be used to add to the mapdata 194 for the PSU 40. This can be used to substantially increase thenumber of map data 194 calculated or collected for each time incrementof collecting the map data 194 with the mapping catheter 100.

In addition, the balloon 102 can be expanded to have an exteriordiameter or geometry greater than an external geometry of the catheter100 and can contact the surface of a structure, such as the heart 80,even though the tip and ring electrodes 108, 110 need not specificallycontact the surface. Accordingly, the balloon 102 can contact a surfacewhile the tip and ring electrodes 108, 110 do not and this allows adetermination of a position of a surface while only measuring impedanceat the tip and ring electrodes 108, 110. This is because the position ofthe surface of the balloon 102 is known relative to the tip and ringelectrodes 108, 110 and points on the surface of the balloon 102 can beused to determine map data 194 based upon the known geometry of theballoon as discussed above.

A mapping catheter 100 that includes the balloon 102 and the electrodes108, 110 can have a substantially fixed geometry near or between theelectrodes 108, 110. The balloon 102 can be expanded to a fixed andknown geometry between the two electrodes 108, 110. Because of the fixedgeometry of the balloon 102, the virtual points 102 p defined by theballoon 102 can be known based upon the measured and determinedpositions of the electrodes 108, 110.

A virtual point on the balloon 102, such as the point 102 p 4, can becalculated to be at a specific axial location between the electrodes108, 110 and at a distance from the longitudinal axis of the mappingcatheter 100, and also at a known angle or orientation relative to themapping catheter 100. The calculation of the virtual point 102 p 4 canbe made substantially continuously with a processor, such as a processorof the PSU 40. In addition, or alternatively, the location of each ofthe virtual points 102 p can be calculated relative to the electrodes108, 110 and collected substantially continuously during themeasurements taken with the electrodes 108, 110. Regardless of themethod, multiple data points can be collected and generated for each ofthe measured impedances with the electrodes 108, 110.

Pathway Icon

A pathway icon 456 can be displayed on the display device 58, asillustrated in FIGS. 22A and 22B. The pathway icon 456 can assist theuser 22 in returning a second instrument or a path previouslyidentified. The path can be generated with a first instrument during afirst time in a procedure. As discussed herein, the pathway icon 456 canbe generated based substantially only or entirely on determinedpositions of the first instrument, such as the mapping catheter 100prior to insertion of a second instrument, such as the lead 120.Accordingly, the pathway icon can be generated only with the PSU 40.

Map data points 198, illustrations of the map data 194, can beillustrated on the display 58 to illustrate a surface of a portion ofthe patient 26, such as a surface of the heart 80. As discussed above,the illustrated surface or information regarding the patient 26 can beused for determining an implantation or positioning of an implant, suchas the lead 120 for an implantable medical device. A lead, such as thelead 120, can be positioned in the patient 26 in any appropriate manner.Nevertheless, the lead, such as the lead 120, is generally positioned inthe patient 26 subsequent to the mapping of the selected portion of thepatient 26 and even subsequent to removal of the mapping catheter 100.The user 22 can determine appropriate or selected positions forimplantation of the lead 120 within the patient 26 using the map datapoints 198 on the display 58.

Information can be displayed relative to the map data points 198 or thesurface 281 on the display 58 to identify a selected location orappropriate location for implantation of the lead 120. The user 22 canidentify points on the display 58 and have an icon illustrated on thedisplay 58 relative to the map data points 198 or the surface 281 toassist in later positioning of the lead 120 relative to the patient 26.As discussed above, the lead 120 can be tracked or its position can bedetermined by the PSU 40 or any other appropriate tracking system.Accordingly, the position of the lead 120 can be illustrated on thedisplay 58 relative to the map data points 198.

As exemplary illustrated in FIG. 22A, the surface 281 can be illustratedon the display 58 based upon the map data 194. The surface 281 can beany appropriate surface, such as a surface illustrating a portion of thepatient's heart 80. A landmark icon 450 can be illustrated relative tothe surface data 281 that can identify or be used as a marker foridentification of a position for implantation of the lead 120. Asdiscussed above, various information can be used to identify theposition for the implantation such as pressure data, motion data, andother data including the map surface 281.

Illustrated in FIG. 22A, as the user 22 withdraws the mapping catheter100, the tip icon 108′ can be illustrated on the display 58. Inaddition, an elongated tube icon 456 can be illustrated relative to thesurface data 281. The elongated tube icon 456 can also be referred to asa driveway or pathway icon to be used during an implantation procedure.The pathway icon 456 can be generated based upon identifying ordetermining a diameter and drawing a three dimensional cylinder or tubearound points determined with the mapping catheter 100. It will beunderstood that the pathway icon 456 can be generated in any appropriatemanner, and can include defining a substantially continuous lineinterconnecting multiple determined position of the electrodes 108, 110of the mapping catheter 100 as it is withdrawn from the patient 26.Also, the pathway icon 456 can be generated and illustrated at anyappropriate time.

The pathway icon 456 can be a substantially three dimensional icongenerated relative to the mapping data, such as the surface 281. Thethree dimensional nature of the pathway 456 can be used to assist theuser 22 in guiding the lead 120 back to the position of the implantationrepresented with the icon 450. As discussed above, removal of themapping catheter 100 from the patient 26 can be performed afteridentifying the location for implantation and representing it with theicon 450. Accordingly, the path of removal of the mapping catheter 100can represent at least one pathway, which can include the most efficientpathway, to return to the implantation site represented by the icon 450.

In addition, the mapping catheter 100 can be placed within the patient26, via a deflectable or steerable sheath, as is known in the art.Accordingly, the removal of the mapping catheter 100 can be through thesheath allowing for a substantially smooth and efficient removal of themapping catheter 100. Although the mapping catheter may be within thesheath, determining a position of the mapping catheter 100 within thesheath can be done with the PSU 40. For example, as discussed herein,the sheath may include a plurality of holes or windows to allow for bodyfluids to enter the sheath to assist in or allowing the mapping catheter100 to measure an impedance within the sheath.

Once the mapping catheter 100 has been removed from the patient, thelead 120 can be positioned into the patient. As illustrated in FIGS. 22Band 22C, the position of the lead 120 can be illustrated on the display58 with an icon 120′. The icon 120′ can identify the position of theimplantable electrode or any other portion on the lead 120. The pathwayicon 456 can be displayed on the display 58 relative to the displayedsurface 281 or any other appropriate data on the display 58. The pathwayicon 456 can identify a selected pathway for moving the lead 120 to theposition for implantation represented by the icon 450.

As illustrated in FIG. 22B, the lead 120, represented by the icon 120′,can be followed or moved along the pathway icon 456 by the user 22. Thesubstantially three dimensional nature of the data can be more easilyvisualized in FIG. 22C that illustrates that the icon 120′, representingthe position of the lead 120, can be illustrated within a threedimensional tube of the pathway icon 456. It will be understood that asingle display, such as the display 58, can illustrate perspective viewsof the pathway icon 456 and the lead icon 120′, as illustrated in bothFIGS. 22B and 22C. Accordingly, more than one view of the lead icon 120′relative to the pathway icon 456 can be illustrated on the display 58.Regardless of the perspective provided, the pathway icon 456 can be usedby the user 22 to assist in positioning the lead 120 to the selectedimplantation site represented by the icon 450.

The mapping data 194 of the patient 26, for example illustrated by thesurface 281, can be substantially three dimensional. Thus, providing athree dimensional view of the pathway icon 456 can assist in assuringthat the appropriate path is followed by the lead 120. The path orposition of the lead 120 can be illustrated by the lead icon 120′. Inmaintaining the lead icon 120′ at a selected position relative to thepathway icon 456 the selected path of the lead 120 can be maintainedwithin the patent 26. This may be helpful if the position forimplantation represented by the implantation icon 450 is within or nearan anatomical feature that may require a specific three dimensionalpositioning or approach of the lead 120.

Cannulation and Surface Refinement

To better illustrate small or hard to find surface features, a blank orsmooth surface can be generated, as illustrated in FIG. 23A. The mappingcatheter 100 can be moved and a surface 480 can be augmented to clearlyshow small deviations relative to a flat or smooth surrounding. Also,additional measurements, such as temperature, can be used to determinelocations of anatomical structures.

The surface 281 can be displayed on the display device 58 to illustratea surface based on the map data collected with the mapping catheter 100or other appropriate instrument. Alternatively, or in addition thereto,map data points 198 can be displayed on the display 58 as well. Thevarious points and surfaces generated and displayed on the display 58are based on, according to various embodiments, positions determined bymeasurements of impedance with the PSU 40. The surface generated basedon incremental or additive measurements can be referred to as a positivesurface. In other words, the positive surface is based upon map data 194that is generated based only upon measurements of impedance by a mappinginstrument, such as the mapping catheter 100 in an additive process. Inthe additive process, each new point is added to the previous set ofpoints and a surface can be generated based upon the complete set ofpoints or any portion of the set of points. Various portions of theanatomy, however, may be hard to visualize or find using an additiveprocess. For example, during positioning of an implant in a left portionof the patient's heart atrium, it may be selected to identify a coronarysinus ostium. Identifying the ostium may be difficult if the position ofthe ostium is not identified.

During the additive process, additional points are added to the mappingdata 194 and illustrated as the map data points 198 or the surface 281.Therefore, depressions or small crevices may be difficult to identifyand enhance. However, if a surface or volume were generated and aportion removed from the volume in a subtractive or inverse process, asmall structure can be easily identified within a large, undisturbedarea. In the subtractive or inverse mapping process, the mappingcatheter 100 can be used to identify points where a surface is not.Accordingly, rather than building or adding to map points 194 or managedor map data points 198, as discussed above, points can be removed fromthe volume or surface to illustrate an area where anatomical structuresare not present. This can be used to identify where an anatomicalstructure is present.

As illustrated in FIG. 23A, according to various embodiments, aninternal view of the surface 281 can be viewed. For example, a slice orcross section 484 can be generated to allow viewing of an interior of asurface or structure, such as an interior of the heart 80. A virtualfilled or pristine volume or surface 480 can also be generated (e.g. agenerated filled volume) in a selected portion of the display 58relative to the surface 281. The volume 480 can be any appropriate shapeor surface geometry and is illustrated as a cube simply for thisdiscussion. Further, the volume 480 is a virtual volume that isgenerated by a processor, such as a processor of the PSU 40 anddisplayed relative to a the surface 281 or map data points 198. A probeicon 482, which can be an icon representing the position of the mappingcatheter 100, can also be displayed on the display 58.

As illustrated in FIG. 23A, the complete volume 480 can be displayed toillustrate a substantially virtual pristine surface or volume relativeto the surface 281. The pristine volume 480 can generally be understoodto be within the volume defined by and over the surface 281, for examplewithin the cutaway or slice view of the surface 281, the cross sectionportion 484. The pristine volume 480 can be positioned at a selectedregion or to cover a selected region, such as a region that may includethe coronary sinus ostium.

With reference to FIG. 23B, the mapping catheter 482 can be movedrelative to the pristine surface 480 to generate a disturbed or inversemapping volume 480′. The inverse mapping volume 480′ can include aninverse or subtracted region 486. The subtracted region can be bound byan edge 488 that can be used to identify a portion of the anatomy of thepatient 26. As discussed above, the coronary sinus ostium may beidentified relative to the patient 26 by a depression or otherappropriate geometry of the patient's 26 anatomy.

Accordingly, the subtracted region 486 can be identified or illustratedas a depression relative to the disturbed volume 480′. The subtractedregion 486 can be determined as that part of the heart 80 that does notinclude a physical wall rather than only a portion of the virtualsurface generated relative to the previously acquired map data. To formthe subtracted region 486, rather than adding map data 198 points ormanaged points to a data set, map data points 198 or managed points canbe removed based upon tracking the position of the mapping catheter 100,as illustrated on the display by the icon 482. As map data points areremoved from the pristine volume 480, to generate the disturbed volume480′, an anatomical region can be identified and illustrated. Theanatomical region can be clearly illustrated and seen relative to theremaining undisturbed portions 490 relative to the subtracted portion486. The substantially sharp edge 488 surrounding subtracted region 486can be used to efficiently or quickly identify portions of the anatomyof the patient 26. The edge 488 can be identified by the user 22 orsubstantially automatically with a processor, such as the processor ofthe PSU 40 or other appropriate processor.

The subtracted portion 486 can be generated substantially similarly togenerating a data set of map data, as discussed above. Rather thanadding map data to a data set, however, map data, map data points 198,or manage points within the pristine volume 480 are removed.Accordingly, the pristine volume 480 can be a complete set of pointswithin a selected region relative to the surface 281. The map data thatis determined with the mapping catheter 100, as illustrated by the icon482, can be those points that are based upon a determined position ofthe mapping catheter 100 by measuring an impedance with an electrode onthe mapping catheter 100. By removing these points from the pristinesurface or volume 480, the subtracted region 486 is clearly illustrated.

The subtracted region 486 can then be illustrated alone, with the othermap data points generated or determined, relative to generated thesurface 281 without a remaining pristine portion 490. By removing theremaining pristine portion 490 from the augmented or disturbed volume480′, a view of the anatomy of the patient 26 can be more usefullydisplayed. As discussed above, the pristine volume 480 is not based uponmapping data relative to the patient 26, but merely describes orincludes a data set of an entire volume of points. Accordingly, thepristine volume 480 is not based upon the patient's 26 anatomy, but isused to efficiently generate the subtracted region 486. Also, thesubtracted region 486 can be illustrated relative to the surface 281either from an internal or external view. As illustrated, the subtractedregion 486 can be viewed from the interior of the surface 281.

Thus, the subtracted region 486 can be used for identifying anatomicalportions of the patient 26, such as the coronary sinus ostium. Thecoronary sinus ostium or other portions can be used for landmarkidentification and performing a selected procedure relative to thepatient 26. Other anatomical depressions or crevices can also beidentified. In addition, a volume can be generated relative to anyportion, as selected by the user 22 or automatically. This can allow theuser 22 to explore any selected region for a depression or crevice asselected by the user 22. For example, the user can examine an area of aninfarct for diseased or necrotic tissue.

In addition to mapping and illustrating the map data points 198 or thesurface 281 on the display 58, various techniques can be used to easilyillustrate various anatomical structures. Identification of the coronarysinus can be used for cannulation of the coronary sinus or placement ofleads in the patient 26 can be performed. Also, other anatomicalfeatures can be identified in the patient 26.

Identification of anatomical features can be for cannulation. Asillustrated in FIG. 24A, the heart 80 generally includes several andvarious anatomical structures. Generally, for discussion of cannulationof the coronary sinus, the anatomical structures can include thesuperior vena cava (SVC) 500, which enters a right atrium (RA) 502 andan inferior vena cava (IVC) 504 that can exit the RA 502. Near the rightatrium 502, a tricuspid valve (TCV) structure 506 separates the RA 502from a right ventricle (RV) 508. Within the RA 502 is the coronary sinusostium (CSO) 510. As discussed above, for a mapping catheter, such asthe mapping catheter 100 including the balloon 102, can be moved throughthe patient 26 to map various anatomical structures. For example,cannulation of the coronary sinus can assist in the identification ofposition and locations for implanting leads into the patient 26. Bypositioning the mapping catheter 100 through the CSO 510 cannulation ofthe CSO 510 can occur.

Various map data points can be illustrated on the display 58 or asurface can be rendered to illustrate cannulation of the CSO 510. Asillustrated in FIG. 24B, a surface 281 c can be used to illustrate theostium of the CSO 510 by illustrating a surface 510′. Any appropriateviews of the surface 281 c can be displayed on the display 58 to providethe user 22 varying perspectives of the surface 281 c.

The data points used to generate the surface 281 c can be generated asthe mapping catheter 100 passes through the SVC 500, illustrated on thedisplay 59 as surface 500′, into the RA 502, illustrated on the display58 as the surface 502′. As illustrated in FIGS. 23A and 24B, the mappingcatheter 100 can be moved through the patient 26 as discussed above. Asthe mapping catheter 100 is moved through the patient 26, the ring andtip electrodes 108, 110 can be used to measure impedance within thepatient 26 to determine or generate the map data points and surface 281,281 c as discussed above.

Alternatively, various other instrumentation can be used such as amapping catheter 520 that includes a balloon 522, as illustrated in FIG.25. The mapping catheter 520 can be any appropriate catheter, such asthe model 6215 catheter sold by Medtronic, Inc. having a place ofbusiness in Minneapolis, Minn., USA. The mapping catheter 520 can bepositioned through a deflectable sheath 524, which can include anyappropriate deflectable sheath such as the model C304 deflectable sheathsold by Medtronic, Inc. having a place of business in Minneapolis,Minn., USA.

A guide wire 526 can also be positioned through a lumen 527 defined bythe mapping catheter 520. The guide wire 526 can be positioned to beexposed and extend a selected distance 526 d, such as about 1 to 2millimeters, past a distal end 522 d of the balloon 522. An exposedportion of the guide wire 526 e can allow the guide wire 526 to be usedto measure impedance within the patient 26. Accordingly, the mappingcatheter 100 can be replaced or augmented with the mapping catheter 520for measuring a bio-impedance or voltage within the patient 26 andgenerating or collecting the mapping data 194 for illustration on thedisplay 58 as the map data points 198 or the surface 281.

The guidewire 526 can include a diameter or other cross-sectionaldimension that is less than that of the catheter, such as the mappingcatheter 100. The guidewire 526, therefore, can be introduced in tosmall enclosures and used to determine fine or small movements of aposition element defines by the exposed portion of the guidewire 526. Tothis end the guidewire 526 can be used to assist in identifying the CSOSand other small areas. The guidewire 526 can, therefore, be used toidentify regions for cannulation or that are cannulated.

It will also be understood, according to various embodiments, that anyappropriate navigation or tracking system can be used to determine mapand data points for display on the display 58. Accordingly, the map datapoints 198 that are displayed on the display 58 can be generated with atracking system such as an electromagnetic tracking system. Theelectromagnetic tracking system can be any appropriate tracking system,such as the Stealthstation® Axiem® System for Electromagnetic Trackingsold by Medtronic Navigation, Inc., having a place of business inLouisville, Colo., USA. The electromagnetic tracking system can be usedto determine a location of the mapping catheter, such as the mappingcatheter 100 or the mapping catheter 520, in any appropriate manner. Forexample, an electromagnetic sensing coil or electromagnetic trackingdevice can be positioned on the mapping catheter 100 or the mappingcatheter 520. According to various embodiments, an electromagnetictracking device can be included or formed within the guide wire 526 totrack the mapping catheter 520 within the patient 26. Similarly, atracking device can be formed within the mapping catheter 100, such as awire coil formed near the tip electrode 108, the ring electrode 110, orat any appropriate location along the mapping catheter 100. Accordingly,the map data points 198 can be generated or determined using anyappropriate tracking system and the PSU 40 can be used to illustrate themap data points 198 or a surface 281 on a display device 58.

The surface 281 can also be updated in substantially real time accordingto various embodiments. For example, a rotating buffer system or anupdate area can be used to illustrate the surface 281 in substantiallyreal time. Techniques for displaying the surface 281 as data points areadded to the surface points 281 are described in co-pending U.S.Provisional Patent Application No. 60/105,597, filed on Oct. 16, 2008and incorporated herein by reference.

In addition to identifying various anatomical structures, such as adepression as discussed above with map data points, other informationcan be acquired regarding the heart 80 of the patient 26 to assist inthe determination of various anatomical structures or features. Forexample, one or more temperature sensors, such as a thermal couple, canbe included on the mapping catheter 100. A thermocouple, thermosistor,temperature sensitive integrated circuits, or other appropriatetemperature measuring devices can be positioned at any appropriatelocation such as near the electrodes of the mapping catheter 100. Bypositioning a temperature sensor on the mapping catheter 100, atemperature signal can be transmitted to the PSU 40 at the location ofthe mapping catheter 100. The position of the temperature sensor can beknown relative to the electrodes of the mapping catheter 100 so that thetemperature of a specific map data point can be determined. Althoughtemperature is an example of any appropriate condition that can besensed, such as pressure, flow rate, etc.

Various regions of the patient 26 can include a temperature differentialbased upon a proximity of an anatomical structure. The anatomicalstructure can be any anatomical structure, for example, the coronarysinus ostium 510 illustrated in FIG. 24A. Coronary sinus drains bloodfrom the heart's circulation so it is generally warmer blood than bloodreturned from the systemic circulation.

As illustrated in FIG. 24C, temperature indicating map data points 510″or surface 510′″ can be displayed on the display 58 relative to themapped data points 198 or the surface 241 of the heart 80. The mappeddata points or area 510″ can include a feature, such as a color,contrast, blink rate, or the like, to identify a temperature relative toother or surrounding surface areas or map data points. As illustrated onthe left portion of the display 58, the temperature map data points 510″can include a color that is darker than the other map data points 198.The color may indicate a higher relative or absolute temperature, whichcan indicate that they are near the coronary sinus 510. A temperature ofthe blood in the region of the coronary sinus 510″ can be higher thanblood in other areas of the heart 80. A threshold can be selected fordetermining whether a different color should be displayed or a gradientof many colors can be selected. Further, rather than a color otherindicia of temperature change can be provided.

When the temperature differential is illustrated on the display 58, suchas with mapped data points or surface 510″, relative to the remainingmapped data points 198 or surface area 241, the user 22 can identify aregion of the temperature differential. The region of the temperaturedifferential can help identify the anatomical structure. The anatomicalstructure can be further displayed on the display 58, such as with theremoved region 486, as illustrated in FIG. 23B. Therefore, it will beunderstood, that multiple information can be displayed on the display 58to assist in identifying anatomical structures and features. It would befurther understood that measuring a temperature in any appropriatelocation of the anatomy can assist in identifying anatomical structuresin that portion of the anatomy. It will be further understood that aprocessor, such as a processor of the PSU 40, can be used to identifyanatomical structures based on the temperature differential.Alternatively, or in addition thereto, the user 22 either alone or withthe assistance of the processor can identify anatomical features basedupon the measured temperature.

State or Location Determination System

The heart 80 of the patient can include one or more measurable featuresor characteristics that can be used to identify or determine a state ora location of the instrument measuring the feature. For example, themapping catheter 100 or the lead 120 can be used to measure pressure oran electrogram (EGM) within the patient 20 to assist in identifying aspecific location within the patient 26. In identifying a locationwithin the patient 26, the user 22 can obtain additional location andorientation information relating to the information displayed on thedisplay device 56, such as a rendering of the map data 194. It will beunderstood that information can be measured at any appropriate locationwithin the patient 26 to assist in identifying a specific locationwithin the patient 26. For example, pressure and an electrogram can bemeasured in any circulatory portion, pulmonary portion, or organ of thepatient 26 with an instrument. The measurement of a characteristic canalso be done manually or automatically at any selected rate, such asonce per heart beat. The discussion herein relating to measuringinformation within the heart 80 of the patient 26 is understood simplyto be an example for the discussion herein.

With reference to FIG. 26A, the mapping catheter 100 can be positionedin the patient 26 at various locations. As illustrated in FIG. 26B,various portions of the heart 80 can be identified in the anatomy of thepatient 26. For example, a superior vena cava SVC, right atrium RA,inferior vena cava IVC, right ventricle RV, a pulmonary artery PA, atricuspid valve TCV, and a pulmonic value PV. Each of the portions ofthe heart 80 can be accessed with the mapping catheter 100.

As particularly illustrated in FIG. 26A, the mapping catheter 100 can beconnected with the PSU I/O 42. In addition, various patient monitoringsystems can include an electrocardiogram (ECG) 570. The ECG 570 can beconnected with the patient 26 using various electrodes exemplaryillustrated as electrodes 572 a-c. Each of the ECG electrodes 572 a-ccan be connected with the ECG 570. The ECG 570 and the PSU 40, in turn,can be interconnected or incorporated. By interconnecting the ECG 570and the PSU 40, information from the ECG 570 can be used by the PSU 40.As one skilled in the art will understand, a cardiac rhythm or cycle canbe measured with the ECG 570 and selected portions of the cardiac cyclecan be determined. Various phases of cardiac cycle can be identifiedautomatically (e.g. by a processor executing instructions and receivinga signal from the ECG 570) or by one skilled in the art viewing a graphproduced from the ECG 570. Various portions of the cardiac cycle caninclude a P-wave, a R-wave, T-wave, and other specific features of thecardiac electrical cycle. The cardiac cycle can also be used to identifyor diagnose conditions of the patient 26.

The ECG electrodes 572 a-c of the ECG 570 can measure or detectelectrical signals from the outside of the patient's body 26, such as avoltage, which can be measured by the ECG 570. As discussed above, theelectrodes of the mapping catheter 100, such as the ring and tipelectrodes 108, 110 can also be used to measure electrical signals ofthe patient 26. Measuring or sensing electrical activity of the patient26 by the mapping catheter 100 can be done in addition or alternativelyto acquiring the mapping data 194. Electrical signals from electrodes inthe body, especially from within the heart, are called electrograms(EGM). The electrodes of the mapping catheter 100 can be used to measureEGMS to be used by the PSU 40. As discussed further herein, a comparisonof a measurement of an EGM with the mapping catheter 100 and ameasurement with the ECG 570 can be used to assist in identifyinglocations of the mapping catheter 100. For example, as one skilled inthe art will understand, various portions of a recorded ECG, such as theP-wave, can be matched or aligned in time to measurements or deflectionswith EGM's measured with the mapping catheter 100 to determine thelocation of the mapping catheter 100. Also, the balloon 102 or otherappropriate sensors can be used to measure pulsative pressure at aselected location of the mapping catheter 100, such as the substantiallynear the distal end.

The mapping catheter 100 can be inserted into the patient 26 through anintroducer, as discussed above, into an axillary vein that extends intothe SVC, as illustrated in FIG. 26B. The mapping catheter 100 cangenerally be understood to substantially always or selectively passthrough the SVC at least in an initial state when introduced through anaxillary vein. The mapping catheter 100 may move into the heart throughthe IVC if it is initially inserted into a leg of the patient 26,however, when the mapping catheter 100 is low in the SVC or the RA, anelectrical measurement or deflection measured with the mapping catheter100 can measure an electrogram (EGM) as illustrated in FIG. 27A. Thevoltage (V) can be plotted over time (T) in a line 580 a. The EGM line580 a can include a large spike or deflection 581 a ₁ which represents aspike in voltage. The timing of the spike 581 a ₁ can be compared to thetiming of a portion of the ECG line 582 a. For example, the position ofthe spike 581 a ₁ of the EGM line 580 a can be compared to the P-Wavespike 583 a ₁. When the spike 581 a ₁ of the EGM 580 a occurs coincidentin time or before the P-Wave spike 583 a ₁ of the ECG 582 a, it is anindication that the electrode measuring the EGM is in the SVC or RA. Asmaller spike 581 a ₂ may also be measured in the EGM line 580 a whichis coincident with the R-wave 583 a ₂ even when the EGM is measured inthe SVC or RA. The smaller spike 581 a ₂ can represent a ventricularactivity.

With reference to FIG. 27B, an EGM line 580 b can be plotted as voltageas a function of time relative to the ECG 582 b, as similarlyillustrated in FIG. 27A. Relatively little or not deflection or measuredvoltage is illustrated. When relatively no or little voltage is measuredby an electrode in an EGM it is an indication that the electrodemeasuring the EGM is either very high in the SVC or very low in the IVC.That is, if the electrode is in the SVC or the IVC it is a relativelylarge distance from the heart, such as an atrium of the heart.

With reference to FIG. 27C, an EGM measuring voltage represented as afunction over time can be displayed as line 580 c. The EGM can includetwo spikes or large deflections 581 c ₁ and 581 c ₂. An ECG line 582 ccan include or illustrate two voltage measurements or deflectionsrepresenting a P-Wave 583 c ₁ and an R-Wave 583 c ₂. If the two spikes581 c ₁ and 581 c ₂ correspond substantially in time with the P-Wave 583c ₁, R-Wave 583 c ₂ an indication can be made that the electrodemeasuring the EGM is in or very near the TCV or the PV.

With reference to FIG. 27D, the electrode can measure the EGM and beplotted as a voltage amplitude line 580 d as a function of time. The EGMcan include a large deflection or voltage spike 581 d. An ECG line 581 dcan also be plotted over the same function of time and illustrates anR-Wave 583 d ₂. If the single large spike 581 d of the EGM line 580 dand the R-Wave 583 d ₂ of the ECG 582 d substantially corresponds ormatch in time it can be an indication that the electrode measuring theEGM is in the RV.

The determination of the location of the mapping catheter 100 can bemade with the assistance of information collected from variousinstrumentation relative to the patient 26 in addition to the mappingdata 194, such as the ECG 570 or recording an EGM with the electrodes onthe mapping catheter 100. The mapping data 194 that is collected withthe mapping catheter 100 can be used to illustrate and identify variousportions of the anatomy of the patient 26. The mapping data 194 can alsobe used to identify various portions of the patient 26. Nevertheless,identifying various portions of the patient 26 independent of or inaddition to the mapping data 194 can be helpful to the user 22.

As illustrated in FIG. 28, the display 58 can include partitions toassist in illustrating various portions of the anatomy of the patient26. For example, a block, square, or other appropriate geometric shapecan be used to surround the map data points 198 within the SVC and theblock can be identified with a label SVC′. It will be understood thatthe map data points or the managed points 198 can be illustrated on thedisplay 58 in any appropriate manner to assist in identification. Forexample, the map data points or surface illustrated on the display 58 ofthe SVC can be illustrated in a different color, intensity, blinkingrate, or the like. Similarly, other markings can be used to illustratethe right atrium, such as a label RA′, the right ventricle, such as thelabel RV, pulmonary artery, such as a label PA′, tricuspid valve TCV′,and the pulmonic valve PV′.

With continuing reference to FIGS. 26A-28, and further reference toFIGS. 29A-29C′, a processor can be used to at least assist inidentifying various portions of the heart 80 of the patient 26. Theprocessor can be that of the PSU 40 or separate therefrom and execute analgorithm or a computer program, including an algorithm, to assist inidentifying, automatically or with input from the user 22, variousportions of the heart 80 or other portions of the patient 26. Accordingto various embodiments, a state machine can be used to assist inidentifying various portions of the anatomy of the patient 26, such asof the heart 80.

Briefly, as listed in FIG. 29A there are only a limited number of statesor locations an instrument can travel (without perforating the heart 80)from any given location in or near the heart 80. FIG. 29B illustrates aflowchart 590 that shows a method that can be used as an algorithm or ina computer program to automatically determine a state or location of aninstrument based on inputs illustrated and described in FIGS. 29C and29C′. The inputs can be automatically received by the processor, such asthe processor of the PSU 40, from electrodes in the heart 80 (e.g. theelectrodes 108,110 of the mapping catheter 100) and the ECG 570. Themethod in the flowchart 590 can be run or processed at any giveninterval, such as once per heart beat. The method of the flowchart 590can also be run or processed with no further intervention from the user22 (i.e. substantially or completely automatically).

As understood by one skilled in the art, by passing through variousnatural openings of the heart 80, the mapping catheter 100 can move fromone particular region to another particular region within the heart 80.From a particular region, such as the superior vena cava, the mappingcatheter 100 can only move to a limited number of other anatomicalregions. A position of the mapping catheter 100 can, therefore, beidentified with measurements taken with the mapping catheter 100, theECG 570, and with reference to previous states or locations of theinstrument (e.g. mapping catheter 100) to identify a location of themapping catheter 100.

As illustrated in FIG. 29A, from selected anatomical locations, aslisted in the left column under “If last known location”, the mappingcatheter 100 can only go to specific other anatomical locations listedin the right column under “Only possible new current location(s)”. Asillustrated in FIG. 29A, from the SVC the mapping catheter 100 can onlygo to the RA. From the RA, the mapping catheter 100 can return to theSVC, or it can go to the IVC, the RV, or the CS. From the IVC, themapping catheter 100 can only return to the RA. From the RV, the mappingcatheter 100 can only return to the RA or go to the PA. From the PA, themapping catheter 100 can only return to the RV. It will be understoodthat each of the current locations can be determined based upon a changeor a measurement that is made. In addition, any appropriate instrumentcan be used, and discussion of the mapping catheter 100 is merelyexemplary. Further, states can be identified for any appropriateanatomical portion, and the heart 80 is discussed here only as anexample.

As illustrated in FIG. 29B, a flow chart 590 is illustrated that can beused to illustrate an algorithm using the state rules illustrated in thechart in FIG. 29A. FIGS. 29C and 29C′ illustrate specific queries andinformation that can be used when determining the state or location ofthe instrument. Reference herein to the determination blocks in FIG. 29Bcan include the various queries and measurements illustrated in FIGS.29C and 29C′. The queries can include position of the instrument, EGMcomparison to ECG (e.g. are any EGM spikes coincident in time with ECGspikes), and pulse pressure (e.g. is a pressure measured that is greaterthan a zeroed or initial pressure). The state determination can be madeat any appropriate frequency, such as with each beat of the heart 80,timestep, etc.

For the current discussion, it will be understood that the mappingcatheter 100, begins within the SVC in block 592. The mapping catheter100 can, however, begin in the IVC. The state changes would be the samefrom the IVC as well. Once it is determined that the mapping catheter100 is in the SVC, measurements can be taken or information regardingthe patient 26 and the mapping catheter 100 can be queried. Initially,the mapping catheter 100 can be determined to be in the SVC byidentifying a substantially concurrent deflection or measurement ofelectrical activity in the patient 26 with the EGM measured by theelectrode of the mapping catheter 100. If the mapping catheter is highin SVC, no EGM signal may be recorded, as illustrated in FIG. 27B. Ifthe electrode is near the RA an EGM signal coincident with P-wave, asmeasured by the ECG 570, may be present as illustrated in FIG. 27A.

A query can then be made in determination block 594 of whether the leadmoved to the RA. As illustrated in FIG. 29B and 29C′, the mappingcatheter 100 can only move to the RA from the SVC. In the determinationblock 594, the determination can be based upon any appropriateinformation. For example, if the EGM measured with the mapping catheter100 has a deflection that substantially coincides in time with theP-wave of the ECG 570, as illustrated in FIG. 27A, that is significantlylarger than a previous measurement, then the YES routine 596 can befollowed to determine that the mapping catheter is within the RA inblock 598. It will be understood that the query in determination block594 can include other measurements or considerations as well. Forexample, the physical location of the mapping catheter 100 can bedetermined to be further inferior relative to the patient 26. Thisindicates that the mapping catheter 100 has moved inferiorly relative tothe heart 80. A further query can be whether a pulse pressure ismeasured. If a pulse pressure is non-existent or determined to not bepresent, such as less than or equal to about 1 mmHg, then the instrumentcan be determined to still be in the SVC. It will be understood that ifeither the three conditions discussed above and illustrated in block 594in FIGS. 29C and 29C′, or any other appropriate conditions, aredetermined to not have been measured or to have not occurred then the NOroutine 600 can be followed to determine that the mapping catheter 100remains within the SVC in block 592. It will be understood, above andherein, that the measured changes may be weighted when determining astate change.

The flowchart 590 can be further followed or analyzed to determine thatthe mapping catheter 100 has moved from the right atrium in block 598 toany other portion of the anatomy, as allowed by the state transitionrules illustrated in FIGS. 29C and 29C′. Once it has been determinedthat the mapping catheter or other measuring portions is within the RAin block 598, further determinations can be made based upon measurementswith the mapping catheter 100. As illustrated in the state chart in FIG.29A, and FIG. 29C′ there are four possible locations for the mappingcatheter 100 to go from the RA. Accordingly, a determination block 602can query whether the mapping catheter 100 went to the SVC, adetermination block 604 can query whether the mapping catheter 100 wentto the IVC, a determination block 606 can query whether the mappingcatheter 100 past the tricuspid valve (TCV) went to the RV, and adetermination block 608 can query whether the mapping catheter 100 wentto the CS.

The SVC, RA, and IVC can all have similar physiological characteristics,as discussed herein. They are, however, separated by inferior andsuperior positioning. Thus, although it can be selected to identifythese three regions as one (e.g. with a single cantor on the display 58)an attempt can be made to distinguish them, as discussed below.

In the determination block 602, the YES routine 610 can be followed ifthere is a decrease in the EGM voltage amplitude that coincides in timewith the ECG P-wave. As discussed above, if there is an increase in theamplitude of the EGM that coincides with the P-wave, the mappingcatheter 100 can be determined to be in the RA in block 598.Accordingly, if there is a decrease in the EGM amplitude that is alignedwith the ECG S-wave, then it can be determined that the mapping catheter100 has transitioned back to the SVC in block 592. This determinationcan be further augmented by measuring a pulsative pressure with themapping catheter 100. Generally, the pulse pressure in the SVC is weak,but can substantially match that in the RA as there is no valve or othermechanical features separating the SVC and the RA. Thus, the pulsepressure may be determined to not be present, as discussed above. Inaddition, as discussed above, the position of the mapping catheter 100can be determined using the PSU 40. As illustrated in FIG. 26A and 26B,the SVC and the RA can be substantially aligned and at a distance fromone another. Accordingly, if the position of the mapping catheter isdetermined to have moved physically from the RA to the locationpreviously determined to be the SVC, this can also be used to determinethat the mapping catheter 100 did move to the SVC in block 602 and theYES routine 610 should be followed.

If it is determined that none of the occurrences in the determinationblock 602 has happened, then the NO routine 612 can be followed to thedetermination block 604 and a query as to whether the mapping catheter100 has moved to the IVC can be made. The queries can include whetherthere has been a decrease in the EGM that coincides with the ECG P-waveor no EGM at all, as illustrated in FIG. 27B. If the decrease in the EGMthat coincides the P-wave is determined or measured, it can bedetermined that the mapping catheter has moved to the IVC and the YESroutine 614 should be followed to the determination that the mappingcatheter 100 is within the IVC in block 616. A second query indetermination block 604 can be if no change in pulse pressure inconjunction with a decrease in the EGM coincides with the ECG P-wave, ifthis is so then the mapping catheter 100 is may be within the IVC inblock 616. Also, the pulse pressure may be determined to benon-existent, as discussed above. A third query can be directed to theposition of the mapping catheter 100. If a decrease in amplitude of theEGM coincides with the ECG P-wave and no pulse pressure change has beenmeasured, but the mapping catheter 100 has moved away from the SVC orhas moved inferiorly within the patient 26, a determination can be madethat the YES routine 614 should be followed to determine or mark thestate that the mapping catheter 100 is in the IVC in block 616.

Turning briefly from the determination of the position of the mappingcatheter 100 from the RA, the position of the mapping catheter from IVCin block 616 can be determined. From the IVC, the mapping catheter 100can only be determined whether or not it has moved back to the RA indetermination block 618. If it has been determined that the mappingcatheter has not moved back to the RA, then the NO routine 620 can befollowed and it can be determined that the mapping catheter 100 hasremained in the IVC in block 616. However, a determination can be basedupon a query of whether an increase in the EGM amplitude coincide withthe ECG P-wave has occurred, as illustrated in FIG. 27A. Also, a queryof whether the mapping catheter 100 has moved closer to the previouslydetermined RA region. Further, a pulse pressure that is non-existent, asdiscussed above, can be used to determine that the instrument has notchanged state. If any of the queries are true, a determination that theYES routine 622 should be followed and the mapping catheter 100 can bedetermined as having returned to the RA in block 598. As illustrated inFIGS. 29A and 29A′, the mapping catheter 100 can only move to one otherstate from the IVC which is to return to the RA.

As noted above, it may be difficult to determine the state of themapping catheter 100, or any appropriate instrument, between the SVC,the RA, and the IVC. As discussed, however, the determination rules ortransition rules identified in blocks 594, 602, 604 and 618, asillustrated in FIGS. 29B, 29C, and 29C′, can be used to attempt to makea determination of the state or position of the mapping catheter 100. Itwill be understood, however, that the position of the catheterdetermined with the PSU 40 can be the most indicative of the location ofthe mapping catheter 100 within the heart 80 as in any of the threestates or locations of the SVC, the RA, and the IVC. As illustrated, theanatomy of the heart 80 is such that the superior venacava is at alocation superior to the right atrium and the inferior venacava. Theright atrium is inferior of the superior venacava and superior of theinferior venacava. Finally, the inferior venacava is directly inferiorof the right atrium and also inferior of the superior venacava.Accordingly, if an initial starting position of the mapping catheter 100is made, such as starting in the superior venacava, if the mappingcatheter 100 is introduced through an axillary vein, then an inferiorand superior position of the mapping catheter 100 can be used to assistin determining its location or state within the heart 80.

Turning back to the determination of whether the mapping catheter hasleft the RA 598 in FIG. 29A′ and FIG. 29B, if it is determined that themapping catheter 100 has not moved to the IVC in block 604, then the NOroutine 624 can be followed to the determination block 606 to querywhether the mapping catheter has moved to the RV. Initially, however,the mapping catheter would first pass the TCV, as illustrated FIG. 29C′.

Prior to the mapping catheter 100 moving into the right ventricle, themapping catheter 100 would pass through the tricuspid valve TCV.Accordingly, when the mapping catheter 100 is in the RA, it can bedetermined that the mapping catheter is on the atrium side of thetricuspid valve. The mapping catheter 100 would then need to move to theventricle side of the tricuspid valve to be in the right ventricle RV.When the mapping catheter 100 is at or near the tricuspid valve or theannulus of the tricuspid valve, a pressure pulse can be measured that isan increase over the pressure pulse measured when the mapping catheter100 is within the RA. At the TCV the pulse pressure may be medium, whichcan be defined as about 5 mmHg to about 15 mmHg. Additionally, an EGMcan include two spikes or amplitude deflections of voltage where one iscoincident with the P-wave and the second is coincident with the R-wave,as illustrated in FIG. 27C. As discussed further herein, an EGM that iscoincident with the R-wave can indicate that the mapping catheter 100 iswithin the RV. However, at the TCV, the EGM can measure electricalactivity of both a right atrium and the right ventricle. Accordingly,the EGM measured with the mapping catheter 100 can include or have twopeaks that coincide with both the R-wave and the P-wave of the ECG.

The determination of whether the mapping catheter has moved to the RV inblock 606 can be based upon whether an increase in pulse pressure ismeasured. If an increase in pulse pressure is measured it can bedetermined that the mapping catheter 100 has moved from the RA to theRV. In particular, if a significantly larger pulse pressure is measuredthen the mapping catheter 100 is likely in the RV. The large pulsepressure can be greater than about 10 mmHg to about 15 mmHg, and includea pulse pressure greater than about 10 mmHg. In addition, the comparisonof the EGM and the ECG can be made. For example, when the mappingcatheter 100 moves into the right ventricle and an EGM is measured withthe electrode on the mapping catheter 100, a large voltage amplitudethat coincides with the R-wave of the ECG is measured, as illustrated inFIG. 27D. Accordingly, if any of the queries are positive, it can bedetermined to follow the YES routine 630 from the determination in block606 to the RV block 632. If the determination is made that the mappingcatheter 100 is moved from the RA to the RV by following the YES routine630, further determinations can be made of whether the mapping catheterhas moved out of the RV in block 632.

The mapping catheter 100, as illustrated in FIG. 29A, following thestate of the mapping catheter 100 from the RV it can move back to the RAor further on to the PA. Turning briefly from the movement of thecatheter from the RA, a first determination can be made as whether themapping catheter has moved from the RV to the RA in determination block634. A decrease in measured pulse pressure can be used to determine thatthe mapping catheter 100 has moved from the RV back to the RA in block634 in FIGS. 29B, 29C, and 29C′. In addition, if the EGM has a largevoltage amplitude that is substantially coincident with the P-wave andif the EGM no longer has a large voltage amplitude that is coincidentwith the R-wave, then the determination in block 634 can follow the YESroutine 636 and determine the mapping catheter 100 has moved back to theRA in block 598. It will also be understood that the instrument wouldagain traverse through the TCV to return to the RA. When going backthrough the TCV an EGM with two spikes coincident with the R and P wavewould be measured, as would an initial pulse pressure measurement ofmedium from large before returning to non-existent.

If none of the determinations are made to be YES, then the NO routine638 can be followed to determination block 640 to determine whether themapping catheter 100 has moved from the RV to the PA. The mappingcatheter 100 can move from the right ventricle to the pulmonary arteryand a determination can be made in block 640. However, prior to themovement of the mapping catheter 100 from the RV to the PA, the mappingcatheter 100 would pass through or be in with the pulmonic valve PVannulus. At the pulmonic valve, an EGM measured with the mappingcatheter 100 can include two voltage amplitudes that are substantiallycoincident with the P-wave and the R-wave, as illustrated in FIG. 27C.The EGM of the heart measured with the mapping catheter at the PV can besimilar to the EGM measured at the TCV. This can be so because themapping catheter 100 is moving from the right ventricle to an area nearthe right atrium. In addition, a pulsative pressure transition from ahigher to a lower pulse pressure can be measured with the mappingcatheter 100 as it moves from the right ventricle to the pulmonaryvalve. The pulse pressure can be measured to be medium (e.g. about 5mmHg to about 15 mmHg) and can be measured to be less than that in theRV, but greater than that in the RA. A second indication can be that theEGM measured with the mapping catheter 100 can be more similar to thatmeasured in the RA, as illustrated in FIG. 27A, but may include some EGMspike coincident with the R-wave as well, as illustrated in FIG. 27C.Accordingly, if the mapping catheter 100 is determined to be previouslyin the right ventricle, the two queries in block 640 can be used todetermine that the mapping catheter 100 has moved to the PA from theright ventricle.

If the determination is made that the mapping catheter 100 has movedfrom the RV to the PA, the YES routine 642 can be followed to thedetermination that the mapping catheter is within the PA in block 644.If the determination that the mapping catheter 100 has not moved to thePA from the RV, the NO routine 646 can be followed. Accordingly, thedetermination can be made that the mapping catheter has remained in theRV in block 632.

Once it is determined that the mapping catheter 100 is within the PA inblock 644, a determination of whether the mapping catheter has returnedto the RV can be made in block 646. In determination block 646, a queryof whether an EGM measured with the mapping catheter 100 has a largedeflection or amplitude that is substantially coincident with the ECGR-wave, as illustrated in FIG. 27D, is made. Additionally, a measurementof an increase in pulse pressure can be queried to determine that themapping catheter 100 has again returned to the RV from the PA. Asdiscussed above, the pulse pressure in the RV is large, as definedabove, and is greater than that in the PA and this increase in pulsepressure can be used to determine that the mapping catheter 100 hasreturned to the RV. If the determination is made that the mappingcatheter 100 has moved from the PA to the RV, then the YES routine 648can be followed to the RV block 632. If it is determined that themapping catheter 100 has not moved from the PA to the RV, then the NOroutine 650 can be followed to determine that the mapping catheterremains in the PA in block 644.

Returning again to a state change or movement of the mapping catheter100 from the RA in block 598, a determination can be made as to whetherthe mapping catheter 100 has moved from the RA to the CS in thedetermination block 608 in FIGS. 29B and 29C. The mapping catheter 100can be used to measure a pulse pressure, as discussed above. From theRA, if a slight or small pulse pressure increase is measured, it can bedetermined that the mapping catheter 100 has moved into at the coronarysinus annulus. The slight or small pulse pressure can be about 1 mmHg toabout 5 mmHg. According to one theory, a physical compression of theballoon 102 of the mapping catheter 100 can be the reason for the slightpulse pressure measurement. The heart, when contracting, can physicallysqueeze the balloon 102 when the balloon 102 is within the coronarysinus. Accordingly, the small pulse pressure increase measured when themapping catheter 100 is otherwise in the RA, can be used to determinethat the mapping catheter 100 has moved to the CS. Also, as illustratedin FIG. 26B, the CS is medial of the RA. Thus, if the position of theinstrument is determined to be medial of the RA or to have moved in amedial direction it can be an indication that the instrument has movedto the CS. A temperature measurement can also be made to determine thelocation of position of the instrument in the CS. As discussed below thetemperature of the blood in and near the CS can be about 0.1 degreeswarmer than the other blood. Further, the direction of flow of blood atthe CS will be away from the CS. As discussed herein, flow direction canbe determined and this can also be used to determine a state or locationof the instrument and the location of the CS. If it is determined thatnone of the above noted measurements or changes occurred, then the NOroutine 660 can be followed to determine that the mapping catheterremains in the RA in block 598. If the determination block 608 is madethat the mapping catheter 100 has moved to the CS, then the YES routine662 can be followed to the determination of the mapping catheter 100 iswithin the CS in block 664.

A determination block can then be used to determine whether the mappingcatheter has moved from the CS in block 664 to the RA in block 598 orhas remained in the CS in block 664. In the determination block 666, thedetermination of whether the mapping catheter 100 has moved to the RAcan be based upon querying if a slight increase in pulse pressure hasbeen removed. As discussed above, a slight increase in pulse pressurecan be used to determine that the mapping catheter 100 has moved intothe CS. Accordingly, if the slight pulse pressure increase is notmeasured any longer, it can be determined that the mapping catheter 100has moved back to the RA and out of the CS. Also, the instrument wouldmove lateral from the CS, in a direction opposite the medial directiondiscussed above. If the determination is made that the mapping catheter100 has not moved to the RA, then the NO routine 668 can be followed todetermine that the mapping catheter 100 has remained in the CS in block664. If the determination is made, however, that the query is positive,the YES routine 670 can be followed to make the determination that themapping catheter 100 is in the RA in block 598.

The flow chart 590 can be used to determine a state or position of themapping catheter 100 as discussed above. A signal to make adetermination can be based upon manual input, a change in a measurement,or a time step or time differential. For example, the user 22 can movethe mapping catheter 100 and an initial a determination of whether themapping catheter 100 is within the patient 26, such as within the heart80, can be made.

The measurements for the determinations discussed above can be made orcollected over a selected period of time, such as one, two, or morecomplete cycles of the cardiac cycle of the heart 80. Also, the timingcan be based upon position sampling timing, such as one or more positionsamples. Position sampling can be at a rate of one per about 80milliseconds (about 12.5 per second). As discussed above, the ECG 570can be connected with the patient 26. The ECG 570 is also connected withthe PSU 40. Accordingly, a portion or number of cardiac cycles can bedetermined based upon ECG 570. In addition, a processor in the ECG 570can identify the various waves of the ECG, such as the P-wave, theT-wave, or the R-wave. Any other appropriate processor can also be usedfor the wave determinations. Further, the wave determinations can bemade manually. It will be understood, therefore, that the position ofthe mapping catheter 100 can be based upon various measurements taken ofthe patient 26, such as with the ECG 570, and include the stateidentifications illustrated in FIG. 29A and other appropriateinformation as discussed above.

The location or state of the various portions of the map data on thedisplay can be updated or corrected. That is that the indication of theparticular state on the display can be corrected to redisplayed at alater timestep. As illustrated in FIG. 28, therefore, the stateindications need not be static.

Further, the flowchart 590 and the related queries are made based onassumptions that the heart 80 of the patient 26 is in normal or sinusrhythm. The ECG, pressure, and other measurements of a sick patient maybe different. Different state information, however, can be used todetermine a state of the instrument is included in the various queryblocks. Also, further inquiries can be added, such as change indiastolic pressure, rate of change of pulse pressure, mean diastolicpressure, and other measurements can be made and queried to determine astate of the instrument. Accordingly, those discussed above areexemplary of queries that can be made when determining a state orlocation of the instrument.

In addition to the various measurements taken with the mapping catheter100 that can be compared to the ECG timing, as discussed above, it willbe understood that the mapping catheter 100 is tracked for positionwithin the patient 26. Accordingly, as discussed above, the inferior andsuperior location of the mapping catheter 100 can be used to assist indistinguishing the SVC, the RA, and the IVC from each other.Additionally, medial and lateral positions can be used to assist indetermining the position of the pulmonary valve and artery from thetricuspid valve and the right atrium. As illustrated in FIGS. 26A and B,the PV and PA are laterally displaced from the TCV and the RA.Accordingly, the position of the mapping catheter 100 can also be usedto assist in determining the position of the mapping catheter 100 anddetermining the state of the mapping catheter 100 within the patient 26.

Anatomical Synchronization

As illustrated in FIG. 26A, the PSU 40 and the ECG 570 can be connectedwith the patient 26. The ECG 570, or any appropriate physiologicalmonitoring system, can be used to measure patient physiologicalfunctions. This information can be used to synchronize the positiondeterminations with physiological cycles of patient functions. Theposition determinations can be those made using the electrodes on themapping catheter 100 to determine a position of the mapping catheter 100within the patient 26. In addition, the reference electrodes 52 a, 52 bcan be used to determine a reference impedance Z52 a 52 b which can beused to determined a position of the reference electrodes 52 a, 52 brelative to the patient 26 and the other electrode patches 46 a-50 b.

The ECG 570 can be used to identify the cardiac cycle of the patient 26and determine in which portion of the cardiac cycle the patient 26presently exists. The reference patches 52 a, 52 b can be used todetermine both cardiac and respiratory cycles of the patient 26 bymeasuring an impedance between the two reference patches 52 a, 52 b,positioned on a dorsal and anterior side of the patient 26.

According to one theory, the reference impedance Z52 a 52 b determinedbetween the two reference patches 52 a, 52 b changes as the heart 80,for example the ventricles, fill and then empty of blood. As isunderstood by one skilled in the art, significant amounts of blood flowto the ventricles and then to the lungs and systemic circulation via theaorta. The blood of the patient 26 is highly conductive relative tosurrounding tissues and other body constituents, such as skeletalmuscle, bone and air. So, as the heart 80 beats and the blood travels inand out of the heart 80, the conductance of the portion of the patient26 in the vicinity of the heart 80 changes as a function of time due tothe shift in position of the bolus of blood being pumped. Accordingly,the change in the reference impedance Z52 a 52 b can be used todetermine or follow the cardiac cycle.

In addition to the heart 80 pumping blood, the pressure in the chest andthorax region can alter based on the respiratory cycle of the patient26. As lungs of the patient 26 fill during inhalation the chest expandsand the relative negative pressure within the thorax decreases. Duringexhalation, for example when the lungs are at peak exhalation, therelative negative pressure in the thorax helps draw blood into theventricles of the heart 80. When the lungs are at peak inhalation, thenegative pressure is less and filling of the heart is less. Also, as thelungs expand and contract, the heart position changes relative to otheranatomical structures, such as the xiphoid process. Accordingly, thevolume of blood within the heart 80, and the related determinedimpedance, during peak inhalation will have a different amount of bloodthan during peak exhalation.

As discussed above, the reference patches 52 a, 52 b can be placed overthe xiphoid process and directly dorsal to the xiphoid process. Asdiscussed above, the heart 80 can moved during inhalation andexhalation. Accordingly, a difference in determined reference impedanceZ52 a 52 b can also be used to determine the position of the heart 80and the respiratory cycle. Moreover, because the reference impedance Z52a 52 b is based on both respiratory and cardiac cycles, the signal ofthe reference impedance Z52 a 52 b can be filtered to determineinformation about both cycles.

The PSU 40 can, therefore, be used alone or with other physiologymonitoring systems to determine both cardiac and respiratory cycles ofthe patient using the impedance and/or information regarding position ofthe reference patches 52 a, 52 b and the ECG 570. The portion of thephysiology cycles can be used to classify the mapping data 194. Forexample, a first map data point can be determined to be within a filling(e.g. diastole) portion of the right ventricle cycle. A second map datapoint can be classified to be within an emptying (e.g. systole) portionof the right ventricle cardiac cycle. Similarly, the map data 194 can beclassified to be within an exhalation or an inhalation portion of therespiratory cycle. Accordingly, each of the map data 194 can beclassified into an appropriate or a selected group based upon thecardiac cycle and the respiratory cycle.

The physiological cycles, however, need not only be split into twogroups or viewed separately. For example, map data can be collected andclassified as (1) in systole and during exhalation, (2) in systoleduring inhalation, (3) in diastole during exhalation, and (4) indiastole during inhalation. Other classifications can also be providedor selected to further segment the map data during collection. The mapdata, however, need not be classified, but can be classified in anyappropriate number of classes for reasons or purposes discussed herein.

With reference to FIG. 30A, once an appropriate data set of the map data194 is collected, based upon a selected class which can be regarding aportion of a selected cycle, such as the diastole portion of the cardiaccycle of the right ventricle, a diastole surface rendering 700 can bedisplayed on the display 58. On or relative to the surface 700 the user22 or the PSU 40 can then identify a first point 702, a second point704, and a dimension 706 between the first and second points, 702, 704for analysis. The points on the surface 702, 704 can be used foranalysis of the heart 80, such as volume change, etc.

With reference to FIG. 30B, an appropriate data set regarding a systolestate of the right ventricle can also be collected and a surface 720,illustrating a systole state of the heart 80 on the display 58 can alsobe rendered. Corresponding points 702′ and 704′ can be determined on thesystole surface 720. A dimension 722 between the two points 702′ and704′ can also be determined for analysis. The points on the surface702′, 704′ can be used for analysis of the heart 80, such as volumechange, etc.

Accordingly, the map data 194, illustrated as the map data points 198 onthe display 58, or as the surfaces 700 and 720 on the display 58 can beselected by the user 22. The user can then view the various surfaces ormodels of the heart 80 to identify lead implants positions, anatomicalfunctioning, and other selected information. It will also be understoodthat the data used to render the surfaces can also be collected indifferent states of the respiratory cycle. Accordingly, the surfacesdisplayed can include different states of the respiratory cycle. Thevarious surfaces, such as the systole and diastole state surfaces, canillustrate differences in the heart 80 based upon a state of the heart80 in the cardiac cycle. This information can be used by the user 22 orany appropriate system to diagnose diseases of the heart 80, implantlead locations (e.g. for optimum stimulation), etc.

As one skilled in the art understands, a position in three-dimensionalspace or patient space, of a portion of the heart, such as an interiorwall position of the right ventricle, is based upon at least the cardiacrhythm and respiration of the patient 26. Accordingly, the map data 194that is collected with the mapping catheter 100 can be identified orclassified to classify the map data relating to the position of thevarious portions being mapped, such as the wall of the heart 80. Thiscan allow for a substantially precise anatomical map of the heart 80 atthe various contraction, relaxation, and respiration positions.

Classifying, saving, and rendering only or substantially only similarlyclassified map data can also allow for a plurality of surfaces to bedetermined, rendered, and displayed on the display 58. According tovarious embodiments, the technique of assigning map data to differentclasses can be used to provide at least a 1) stable display of theheart, 2) video or motion “image” synchronized to the patient's 26physiology, or 3) slow motion video or motion image without reference toany current patient 26 physiology. The motion of the heart 80 and thevarious instruments, such as the mapping catheter 100 within the heart80, imparts information utilized by the user 22. The motion can begenerated by display successive images of map data that are classifiedas successive parts of a respective cycle or multiple cycles. Theresulting map data points or surface can be used to illustrated anatural and true position and movement of the heart 80. It will beunderstood, however, that map data can be collected for any appropriateregion of the patient 26 and the heart 80 is merely an example.Nevertheless, the image on the display 54 need not be a static imagethat relates only to an average of maximum distance within the heart 80,but can be a moving image based on a successive display of multiplerenderings of the map data classified from the patient 26.

As one example, a stable image of the heart can be rendered from data ofa particular or single selected map data class (e.g. diastole andexpiration). Such an image can impart great understanding and confidenceby the user 22. Rendering of the instruments, such as the electrodes108,110 of the mapping catheter 100, can also be presented with the sameclassification so the representation of physical position is in the samecontext as the rendered image of the heart chambers/vessels.

A motion video, such as one generated by sequential morphing of stableimages synchronized to the patient's 26 physiology can mimic a positionof the heart 80 and motion as it occurred when the map data weregathered, classified, and stored. While particular care can be takenduring changes in rhythm, such as sighs or extrasystolic cardiacactivity, such a motion video allows rendering of the instruments, suchas the mapping catheter 100, to be essentially in real-time. That is,localization of electrodes or other sensors can be drawn to the display54 as they are received and super-imposed over a moving background. Thiscan be compared to the stable image of the heart 80 which can be drawnfrom the same classification of the map data. Displaying motion of theinstrument super-imposed on a stable or fixed image may be confusing;that is, it may show the lead moving and penetrating a wall of the heart80 when, in reality, the heart 80 is in motion, but not shown as such onthe display 54. Playing a video as a background image on which theinstrument position is displayed assumes the heart position and motionremain the same as when the data were acquired. While this may not beprecisely true, it can provide information to the user 22 not seen orprovided with a stable image based on unclassified data or only a singleclass of map data.

A slow motion video of the heart 80 and instruments could help the user22 understand the data being presented. This could be a replay of thesaved map data so the relative positions of the heart and instrumentscan be easily seen. Such video could be selected from recently saved mapdata and replayed during an implantation procedure. In addition, the mapdata can be replayed for training, review, or planning purposes.

As a further specific example, map data can be gathered for anyappropriate portions of the cardiac cycle and respiratory cycle. Thedifferent classified data can then be displayed on the display 58, asillustrated in FIGS. 30A and 30B, to illustrate the surface rendering700, 720 of the heart 80 at different cardiac cycle positions. Aselected number, such as 2, 4, 16, or any appropriate number, ofrenderings can then be displayed in succession or synchronized with theECG 570 or displacement between two electrodes such as xiphoid and back.This can allow the display on the display 58 to substantially mimic thecardiac cycle and respiration cycle of the patient 26.

The surfaces 700, 720, can be based on rendering the map data 194collected with the mapping catheter 100. Image data, collected with animaging system, external to the patient 26 or separate from the PSU 40and the mapping catheter 100, need not be required to generate thesurfaces 700, 720, illustrated in FIGS. 30A and 30B. Nevertheless, thedisplay on display 58 can be used to display a substantially correctanatomical position of the heart 80 based on classifying the map data194 to the cycle of the patient, such as the cardiac and respirationcycle. Thus, the surface rendering on the display 58 can be generated toshow sequential motion, and other appropriate information to the user 22without requiring an external imaging system to continuously image thepatient 26.

Bi-Polar and Uni-Polar Measurements

As previously discussed, the mapping catheter 100 can include twoelectrodes, such as the tip electrode and the ring electrode 108, 110.When both electrodes are exposed bipolar measurements can be made andwhen only one is exposed, unipolar measurements can be made. The twoelectrodes of the mapping catheter 100 can be delivered to the patient26 in a specific location through a sheath or other sleeve portion. Whenthe two electrodes are within the sheath, either no electrodes or onlythe tip electrode 108 is exposed to fluids that allow the electrode tomeasure an impedance or voltage within the patient 26. When both of theelectrodes, including the tip and ring electrodes 108, 110, are exposedthen both electrodes can measure an impedance within the patient. Inaddition, other instruments positioned within the patient 26 can includeone or more electrodes to measure an impedance. The electrodes 108, 110of the mapping catheter 100 can also be used to measure electricalactivity within the patient 26, such as measuring electrical activity inthe heart 80 of the patient 26 to generate an electrocardiogram of thepatient 26.

Because the number of electrodes exposed to the anatomy of the patient26 can differ over time, the PSU 40, including the PSU I/O 42, candetermine whether the system PSU 40 should measure, such as the EGM, ina unipolar or bipolar manner. When two electrodes are exposed, the PSU40 can measure in the bipolar manner, such as an EGM or an impedance ofthe patient 26. When only one of the two electrodes is exposed, then thesystem PSU 40 can measure in a unipolar manner. Accordingly, the PSU 40and other appropriate systems can measure in a uni-polar or bi-polarmanner (e.g. measuring with one electrode or two or more electrodes) andcan be switched, manually or automatically, between uni-polar andbi-polar.

The PSU 40 can switch between a unipolar and bipolar manner based uponvarious inputs. For example, the user 22 can input when the lead or themapping catheter 100 is being pushed past the end of a sheath or otherisolating covering. Accordingly, a substantially manual input can beused to instruct the system PSU 40 to measure in a unipolar or bipolarmanner.

The PSU 40 can substantially automatically determine whether to measureeither unipolar or bipolar, depending upon the number of electrodesexposed. The PSU 40 can determine that two electrodes are exposed whentwo electrodes measure impedance and/or EGM at a time step that aresubstantially identical, when at a substantially immediate time step theEGM and/or impedance was substantially different. In this manner, whenone electrode is exposed to the body fluids of the patient 26, animpedance can be measured while the other substantially insulatedelectrode is not measuring an impedance within the patient 26. At asecond time step, when the second electrode is exposed to the patient26, it can measure the impedance of the patient 26. In addition, whenboth electrodes of the mapping catheter 100 are exposed, the impedancemeasured by both should substantially match. Other appropriate methodscan be used to determine when electrodes are exposed or pushed past theend of the sheath, such as those disclosed in U.S. patent applicationSer. No. ______ (Attorney Docket No. 5074D-000062), incorporated hereinby reference.

When switching between measuring the EGM or the impedance in the patienteither in a bipolar or unipolar manner, differences or similarities canbe measured. For example, the impedance of the patient measured with thefirst and second electrodes, such as the tip electrode 108 and the ringelectrode 110 of the mapping catheter 100, that are near each other thenthe impedance measured of the patient 26 should be substantiallysimilar. Therefore, a confidence measure can be obtained when anappropriate measurement is taken. In addition, an EGM measurement can bechanged between a bipolar and unipolar measurement such as bydetermining when an electrode is withdrawn. For example, when anelectrode is insulated or withdrawn into a catheter, the EGM signaldisappears.

Flow Direction

Direction of flow of material within the patient 26 can be determinedwith the PSU 40, according to various embodiments, as illustrated inFIGS. 31A-34B. In addition, the flow of material within the patient 26can be displayed on the display 58, also according to variousembodiments. The direction of flow of material within the patient 26 canbe used for various purposes, such as determining a location of thecoronary sinus, other openings, flow of material within a vessel orvasculature, or other information. The direction of flow can be used toidentify the coronary sinus ostium (CS OS) within the heart 80. Theidentification of the CS OS can be used to assist in identifyinglocations of appropriate implantation of a lead, such as within the leftportion of the heart 80, and can be used to identify unexpected flowdirection associated with congenital abnormalities of the circulation.Thus, flow direction can be used to identify or diagnose variousillnesses.

With reference to FIGS. 31A and 31B, a mapping catheter 100 can bepositioned within the patient 26, such as within the heart 80. Asdiscussed above, the mapping catheter 100 includes electrodes that canmeasure an impedance within the patient 26 for position determinationwith the PSU 40. The direction of flow or movement within the patient26, such as within the heart 80, can be calculated based upon themovement of the electrodes 108, 110 of the mapping catheter over time.The electrodes 108, 110 can move while holding steady or at a staticlocation a portion of the mapping catheter 100, such as a proximal endof the mapping catheter 100. Thus, movement of the electrodes 108, 110can be substantially or only because of flow of a material at a distalend of the mapping catheter 100.

For example, as illustrated in FIG. 31A, at a first time, a tipelectrode point 108′, representing a position of the tip electrode 108,can be determined relative to a point 740 on a portion of the surface281. A distance 742 can be calculated between the two points 740, 108′.At a second time later than the first, such as at a fraction of asecond, a complete second, or any appropriate portion of time, a secondposition or point 108″ of the tip electrode 108 can be determined and asecond distance 744 relative to the same point 740 on the surface 281can be calculated.

The difference between the two distances 742 and 744 can be used tocalculate an amount of flow or force of flow. The direction of movementof the tip electrode 108 can also be determined based upon the twopoints 108′, 108″ to determine a direction of flow relative to the point740 on the surface 281. Accordingly, a direction of flow and anindication of force of flow can be calculated based upon the change inposition of the mapping catheter 100 over time.

The balloon 102 can be used to assist in determining the direction offlow by causing resistance within the flow within the patient 26. Asdiscussed above, the balloon 102 can be inflated once positioned withinthe patient 26 and the balloon 102 can have a cross section greater thanthat of the remaining portions of the mapping catheter 100. The balloon102, with its large area, can cause drag relative to the electrodes 108,110 of the mapping catheter 100 to assist in a flow direction and forcedetermination. The flow of material, such as blood, can drag the balloon102 to determine motion.

Flow direction within the patient 26 can also be determined by aphysical difference between two points. Because the PSU 40 allows for adetermination of a three dimensional position of an electrode positionedwithin the patient 26, based upon the measured impedance or voltagewithin the patient 26. Accordingly, if two electrodes are positionedrelative to one another and a flow is allowed to act on at least one(i.e. a moveable electrode) of the two electrodes, a direction ofmovement of the moveable electrode relative to the substantially morestationery electrode can be determined. The two electrodes on themapping catheter 100 can be selected to move relative to one another toassist in determining flow direction. Nevertheless, other devices or anaugmented mapping catheter 100 can be provided.

For example, as illustrated in FIG. 32 a mapping catheter 750 isillustrated. The mapping catheter 750 can be similar to the mappingcatheter 100, discussed above, and can include more than one electrodeor the balloon 102, like the mapping catheter 100. The mapping catheter750, however, is discussed as including only a single catheter electrode752 for simplicity of the current discussion. The mapping catheter 750can include a sheath or cannulated tube 754 that can be positionedwithin the patient 26. Passing through an inner cannula or passage 756can be a second flexible electrode body 760. The flexible electrode body760 can include an electrode tip 762 and a length that can be insulatedwith a covering 764. The electrode tip 762 can be used to measure animpedance or voltage within the patient 26, similar to the electrodesdiscussed above, such as the tip and ring electrodes 108, 110 of themapping catheter 100.

The catheter electrode 752 can be used to measure a first position andthe flexible member electrode 762 can be used to measure a secondposition. The flexible member electrode 762 can be allowed to flex andmove relative to the catheter electrode 752 based upon a flow ofmaterial within the patient 26. To allow the flexible member electrode762 to move relative to the catheter electrode 752, the flexible member760 can be formed of any appropriate material that is flexible enough tomove when influenced by a flow of material within the patient relativeto the catheter electrode 752. Also, the outer portion 750, particularlya distal end thereof, can be held at a static location within the heartother appropriate volume during flow or motion determination. Accordingto various embodiments, the flexible member 762 can be formed of asubstantially small diameter wire that can be formed of any appropriatematerial, such as gold or copper. In addition, it will be understoodthat the dimensions of the mapping catheter 750 and the flexible member760 are illustrated simply for clarity and can be provided in anyappropriate dimensions. For example, the flexible member 760 can have anexternal diameter that substantially fills an internal diameter of thecannula 756.

As illustrated in FIG. 33, a mapping catheter 750 a can include aninternal cannula 756 a that has an interior diameter that substantiallymatches an external diameter of the flexible member 760. Accordingly,the flexible member 760 can be held substantially fixed relative to acatheter electrode 752 a save for forces acting upon the portion of theflexible member 760 extending from a distal end 770 of the mappingcatheter 750 a. Accordingly, substantially only flow motion will beindicated based upon a position of the flexible member electrode 762relative to the catheter electrode 752 a.

With reference to FIGS. 34A and 34B, the mapping catheter 750 a can bepositioned within the patient 26, such as within the right atrium of theheart 80. Once the mapping catheter 750 a is positioned within the heart80 (or at any appropriate time), the flexible member 760 can be extendeda selected distance out of the catheter body 754 a. Once the flexiblemember 760 is extended out of the catheter body 754 a, such as aselected distance from the distal end 770, flow within the heart 80 cancause the flexible member 760 to bend or move. The flexible memberelectrode 762, being positioned substantially at a distal end or at anyappropriate position on the flexible member 760 that is able to moverelative to the distal end 770 of the catheter body 754 a, can movewithin the flow. Once the force of the flow acts upon the flexiblemember 760 to move the flexible member electrode 762, the PSU 40 candetermine the position of both the catheter electrode 752 a and theflexible member electrode 762 a.

As illustrated on the display 58 in FIG. 34B, a mapping catheterelectrode icon 752 a′ can be displayed on the display 58 relative to themap point 194, such as the surface 281. It will be understood, however,that determining a flow direction does not necessarily require other mapdata 194 to be illustrated. The surface 281 is displayed forillustration purposes and this discussion as an example.

The PSU 40 can also illustrate a position of the flexible memberelectrode 762 as flexible member electrode icon 762′. The user 22 canthen view on the display 58 the position between the mapping catheterelectrode icon 752 a and the flexible member electrode icon 762 to viewa direction of flow. In addition, the PSU 40 can determine a directionof flow based upon the difference in position of the determinedpositions of the electrodes of the mapping catheter 752 and the flexiblemember 762. The direction of flow can be illustrated as an icon, such asan arrow icon 780. The arrow icon 780 can illustrate the direction offlow in a selected area. For example, flow of blood within the heart 80may be away from the CS OS, but blood may flow in any various directionsat other locations within the heart 80. It will be understood, that thedirection of flow may also change based upon the position within thepatient 26. Accordingly, one or more flow direction icons, such asarrows 782, 784, and 786 can be displayed on the display 58.

According to various embodiments, the display 58 can include any and allof the data discussed above. In addition, the display 58 can bemanipulated according to any method, as discussed above. Accordingly,the rocking can be instituted to illustrate the substantially threedimensional nature of the varying positions for the flow direction asillustrated on the display in FIG. 34B. This can allow the user 22 toillustrate a two dimensional or three dimensional view of the mappingdata and the flow direction determination. In addition, the position ofthe various electrodes, such as the mapping catheter electrode 752 a andthe flexible member electrode 762, can be done in substantially realtime. This allows the display 58 to be updated in real time toillustrate the change in flow over time. The display 58 can also be usedto display a plurality of flow directions in a single location overtime. Accordingly, the user 22 can view a turbulent area and understandthe turbulence in the single area based upon a plurality of flowdirection measurements. Turbulence may be due to valvular dysfunctionresulting in regurgitate flow.

Additionally, the force of flow can be determined based upon the amountof bending of the flexible member 760. The amount of bending can bebased upon the known dimension of the flexible member 760 extended pastthe distal end 770 of the mapping catheter body 754 a and the positionof the flexible member electrode 762 relative to the mapping catheterelectrode 752 a. The further the flexible member electrode 762 isradially displaced from the mapping catheter electrode 752 a, thegreater the force of flow within a particular area can be inferred ordetermined.

In light of the above, the PSU 40 can be used to identify various pointsand/or locations and illustrate the various points on the display 58. Byidentifying a plurality of points and plotting or determining a locationof each of the points relative to one another in a three dimensionalspace, a map is generated. As discussed above, the map can beillustrated on the display 58 as the map data points 198 or the surface281. In addition, the PSU 40 can be used to identify and illustrate thelocations of various landmarks or features within the patient 26, asdiscussed above.

Sheathing Detection

As discussed above, an electrode positioned within the patient 26 can beused to sense or measure a voltage and/or determine an impedance. Thevoltage or impedance can be used to determine a position of theelectrode within the patient 26. The position of the electrode withinthe patient 26 can be illustrated on the display 58 and a map can begenerated from the position data.

According to various embodiments, however, as illustrated in FIG. 3, themapping catheter 100 can be introduced into the patient 26 through asheath 104. The sheath 104 can substantially insulate the electrodes onthe mapping catheter 100 such that the electrode does not properly sensethe voltage within the patient 26, therefore altering the determinedposition of the catheter and electrode within the patient. Similarly, anelectrode that is a retractable electrode can be retracted into aninsulative housing thereby substantially rendering immeasurable anyvoltage and impedance determination.

Accordingly, it can be selected to include an algorithm or method thatdetermines whether the electrode used for mapping or positiondetermination is properly exposed within the patient 26. According tovarious embodiments, the PSU 40 can identify whether an electrode issheathed or unsheathed. As discussed herein, a sheathed electrode can beany electrode that is covered by an insulator, such as a sheath fordelivering the catheter or introducing the catheter. An unsheathedelectrode can be any electrode that is exposed to a conductive mediumwithin the patient 26 for properly sensing a voltage to determine animpedance.

With reference to FIG. 35, the display 58 can illustrate whether thecatheter (e.g. an electrode moveable relative to the catheter), leadelectrode that is retractable into a sheath, or other position elementhas been determined to be sheathed or unsheathed. As illustrated inscreen 58 a, a representation of a portion of the mapping catheter 100is illustrated. The mapping catheter 100 can be illustrated as includinga sheath portion 108 and an extendable electrode portion 102 x. It willbe understood that the icons 108 and 102 x can be provided orillustrated in any appropriate color or grey scale. For example, asillustrated in FIG. 35, the sheath icon 108 can be shown heavierbordered or in a different color than the electrode icon 102 x, whichcan be illustrated substantially empty or only as an outline. Inaddition, the map data points 198 can also be displayed relative to theicons 108 and 102 x. If it is determined, as discussed herein, that themapping catheter 100 is sheathed, an alternative display 58 a′ candisplay a sheathed icon 102 x′. The sheathed icon 102 x′ can differ fromthe electrode icon 102 x in color, shading, or grey scale, and isexemplary illustrated as a hatched icon, but may also be illustrated asa bright red or orange. The sheath icon 108, however, can remain thesame color, shade, etc.

It will be understood that the unsheathed icon 102x can be illustratedin a blue, green, grey, or other appropriate color. The sheathed icon102 x′, however, can be illustrated in a generally understood warningcolor such as red, yellow, orange, or the like. Regardless of theillustration, however, the display 58 can be used to identify orcommunicate to the user 22 that the mapping catheter or electrode issheathed or unsheathed. Also, auditory warnings can be given to the userin addition to visual warnings that the mapping catheter or electrodehas become sheathed.

According to various embodiments, measurements of the position, eitherrelative or absolute, of the various mapping electrodes can be used todetermine whether the electrodes are sheathed or not. One or morealgorithms or methods can be used to determine whether an electrode ofthe mapping catheter 100 is sheathed or not. Accordingly, althoughmultiple algorithms are disclosed or discussed herein, only one or anyappropriate number can be selected to be used for sheath or unsheatheddetection.

It will also be understood that if an electrode is sheathed, theposition information may not be reliable or valid. Accordingly, if it isdetermined that the mapping catheter electrode of the mapping catheteris sheathed, it can be determined that the position information basedupon the sheathed mapping catheter is not used or should not be used ingenerating the map data points 198 or surface that is displayed on thedisplay 58.

Any appropriate time scale can be used to determine whether informationis used to generate the map on the display 58, such as one or more timesteps for collecting position information of the mapping catheter 100.Generally, the position of the mapping catheter can be sampled at aboutone sample per 80 milliseconds. For various purposes, detection ofwhether a mapping catheter is sheathed or unsheathed or has becomesheathed can be selected to occur within one time period or at any otherappropriate time period, such as two, three, or other sampling rates.For example, if it is selected that the determination of whether themapping catheter has become sheathed and the position information shouldnot be used, ten samples can be used to determine whether a particularposition sample is valid or not.

An algorithm for sheath detection can be based upon various observationsor determinations. Observations can include at least the following fiveobservations:

1. If an electrode travels drastically further between two successivetimesteps, whether immediate or not, than it did between previoustimesteps, then an electrode has likely become sheathed.

2. If two electrodes belonging to the same instrument travel in verydifferent directions, then the instrument has likely become sheathed.

3. If two electrodes belonging to the same instrument travel in verydifferent amounts, then the instrument has likely become sheathed.

4. If the inter-electrode spacing on an instrument expected or known tobe relatively closely spaced and inflexible has become very large in anabsolute sense or relative to prior samples, then the instrument haslikely become sheathed.

5. If the electrode or instrument is determined to have gone past amaximum distance, especially if over a selected period of time, it haslikely become sheathed.

Each of the five observations can be encoded in a computer-readableprogram and follow an algorithm, as discussed further herein. Any or allof the five observations can be used to determine that one or moreelectrodes or an entire instrument (e.g. the mapping catheter 100) issheathed. Further, the observations can be used to compare one or moresamples of position information or data as discussed further herein.

With reference to FIG. 36, a general algorithm for sheath detection isillustrated in the flowchart 800. The method can begin in Start block802. In a determination block 804 it can be determined if the electrodeis sheathed, as discussed below according to various manners. If it isdetermined that the electrode is unsheathed, the NO path 806 can befollowed and Map data can be collected and saved in block 808. Asdiscussed above, the collected map data can be displayed on the display58 for various procedures and purposes. The method 800 can then end inblock 810.

If it is determined that the electrode is sheathed, according to any ofthe various manners discussed below, then the YES path 812 can befollowed. The electrode can then be marked as sheathed and position datacollected while the electrode is sheathed can be disregarded in block814. The method can then proceed to unsheathing the electrode in block816. Once the electrode is unsheathed, map data can again be collectedand saved in block 808 and the sheath detection method can end in block810.

Any or all of the manners discussed herein can be used to determine ifan electrode is sheathed. Also, the determination can be made that allor less than all of the electrodes on an instrument are sheathed. Theelectrode or instrument that is then marked as sheathed can beillustrated on the display 58 in any appropriate manner, as discussedabove.

In one manner of sheath detection, determining if an electrode hasbecome sheathed can be based on an apparent determination that theelectrode travels drastically further between two successive timestepsthan it did between two or more previous timesteps. To make thedetermination, the PSU 40 can determine a vector relating to one or moreelectrodes for each incoming sample. A present vector, relating to thepresent time step, and all previous or selected number of time steps isrecorded. If the present vector is significantly larger, such as atleast a significance threshold, than a previous vector for a selectedelectrode, the selected electrode is marked as sheathed. It will beunderstood that any appropriate number of electrodes can be so testedand marked as sheathed or not. Generally, however, if at least oneelectrode of an instrument is determined to be sheathed then the entireinstrument is marked as sheathed.

The significance threshold can be any selected and appropriate value.Also, the significance threshold can vary depending upon the size ofprevious vectors. Generally, a relationship of whether the presentvector is significantly larger than the previous vector is inverselyproportional to the magnitude of that vector. So if the vector is smallthen the value of the significance threshold has to be high; and if thevector is large, the significance threshold should be low. This isgenerally so because if the electrode is relatively still within thepatient 26, there could be very little movement. Once the user moves theelectrode, such as of the mapping catheter 100, the new motion could bemagnitudes larger than previous motion, however it has not beensheathed. If the user is moving the electrode quickly and it becomessheathed, then the amount of motion due to sheathing may not be muchlarger than the natural motion due to operation by the user.

In order to account for the relationship between the vector magnitudeand the threshold, a determination can be made if the current distancetraveled or vector magnitude is at least 4.5 times that of the previousmovement or vector raised to the fourth power. In other words, if themagnitude of the previous vector of the electrode was determined to be 2mm, which raised to the 4th power is 16 mm, and the current vector has amagnitude of 72 mm or more, then a determination that the electrode hasbecome sheathed can be made by the PSU 40. Other appropriate thresholdscould be selected, such as a multiplier of more or less than 4.5 or apower of more or less than 4.

Once it is determined that an electrode is sheathed, data collected isdetermined to be invalid. Valid data is not collected and used by thePSU 40 for mapping until the electrode is determined to be unsheathed.Once the PSU 40 determines that the electrode is sheathed thedetermination remains until an unsheathed determination is made. Thesheathed determination is maintained until the electrode approaches aselected radius of the electrodes last known unsheathed location. Inother words, when the electrode is determined to be near a point wherethe electrode was previously unsheathed it can be determined that theelectrode has moved out of the sheath. This radius can grow over time into compensate for natural movement which may occur as the electrode issheathed.

In various manners, an electrode can be determined to be sheathed if twoelectrodes s are relatively close and on a rigid portion belonging tothe same instrument, such as the lead or the mapping catheter 100,travel in very different directions. The two electrodes can be the tipand ring electrodes of the mapping catheter 100. The process for makingthe determination that two electrodes travel in significantly differentdirections can begin with determining the unit vector describing thedirection of travel for the tip 108 and ring 110 electrodes. Asdiscussed above, the ring electrode 110 is proximal and closer to thesheath 104 than the tip electrode 108. Initially, if the tip electrode108 has moved a very small amount (e.g. less than about 2 mm, or lessthan about 1 mm), this process is deemed inaccurate as the determinedmotion could be due to noise in the PSU 40 system. Thus, the sheathedattribute for the ring electrode 110 is left unchanged by this process.If the determined movement of the tip electrode 108, however, is abovethe selected initial threshold then a dot-product is determined betweenthe vectors of the tip electrode 108 and the ring electrode 110 tocalculate the similarity in direction of travel. If the dot product isbelow a dot-product threshold then the ring electrode is marked assheathed. The dot-product threshold can be selected by the user orautomatically selected by and programmed into the PSU 40. For example,the dot-product threshold can be 0.25. It will also be understood thatthe instrument, such as the mapping catheter may include more than onering electrode and, therefore, this process is repeated for each ringelectrode.

Again, once an electrode has been marked as sheathed, it is not markedas unsheathed until an unsheathed occurrence is calculated. In thiscase, the electrode can be determined to be unsheathed if the tip-ringdistance returns to some unsheathed factor of the last known goodtip-ring distance. This unsheathed factor increases as time passes toaccount for non-linearities in the current fields generated in thepatient 26 by the PSU 40, which may cause the tip-ring distance tonaturally grow.

According to various manners, a determination that an electrode hasbecome sheathed can be made if two electrodes belonging to the sameinstrument, such as the mapping catheter 100, travel significantlydifferent amounts, e.g. past a movement significance threshold. To makethe determination if the amount of movement is significantly different,the distances of travel for the tip and each ring electrode aredetermined. Again, if the tip has moved a very small amount, thisprocess is deemed inaccurate as motion could be due to noise. Thus, thesheathed attribute for the ring electrode is left untouched by thistest. Otherwise distances are compared to see if the ring electrodemoved significantly further than the tip electrode.

The movement significance threshold can be selected by the user,automatically selected, or preselected. For example, the movementsignificance threshold can be a difference of three times. Thus, if thetip electrode is determined to have moved at least three times thedistance of the ring electrode, the electrode can be marked as sheathed.Any appropriate movement significance threshold can be selected however,such as two times.

Again, once an electrode has been marked as sheathed, it is not markedas unsheathed until an unsheathed measurement is made. In this manner,the tip-ring distance is determined to have returned to some gooddistance unsheathed factor of the last known good tip-ring distance.This good distance unsheathed factor increase as time passes to accountfor non-linearities in the current fields generated in the patient 26 bythe PSU 40, which may cause the tip-ring distance to naturally grow.

According to various manners, the electrode may have become sheathed ifthe inter-electrode spacing on a single instrument, such as the mappingcatheter 100, has become significantly larger in an absolute sense orrelative to prior samples. As discussed above, the position of theelectrodes, such as the tip electrode 108 and the ring electrode 110 canbe determined. Thus, a distance between them can also be determined. Thedistance between them can be an absolute value, such as 1 mm measured atany time in the patient 26, or a relative value when comparing twomeasurements. As discussed above, the distance between the tip and thering electrodes, 108, 110 can be determined or corrected according to atip-ring correction method. Determining the ring electrode is sheathed,however, can be an alternative determination as rather than simplycorrecting for distortions of the current fields in the patient 26generated by the PSU 40.

The sheath detection method, can begin with determining and/or savingthe distance between each electrode and its neighbor on the instrument.If the distance is above some absolute distance threshold then theproximal electrode (e.g. tip electrode 108) in the inter-electrode pairis marked as sheathed. This can be the absolute distance determinationor portion of the sheathed determination process. The absolute distancethreshold can be any appropriate distance, can be a known or initiallymeasured distance. For example, it may be known that two electrodes are5 mm apart. Thus, the absolute distance threshold can be 5 mm.

If the absolute distance threshold is not reached, the inter-electrodespacing is compared to a previous sample to determine that a relativedistance threshold has been reached. The previous sample could be animmediately previous sample or any appropriate previous sample. If therelative distance threshold is reached, then the proximal electrode inthe pair is marked as sheathed.

The relative distance threshold can be any appropriate value. Generally,the significance of the relative distance threshold can relate todistance. The smaller the inter-electrode distance, the more it has togrow to be considered sheathed. Hence the relative distance thresholdcan be if the square of the current interelectrode distance is 2.5 timesgreater than the immediately previous interelectrode distance, theelectrode can be marked as sheathed. For example, if the currentinterelectrode distance is 5 mm, its square is 25 mm. Thus, if theprevious interelectrode distance is 10 mm or less than the electrode ismarked as sheathed.

Again, the electrode is determined to remain sheathed until ameasurement is made that the interelectrode distance has returned tosome good interelectrode distance factor. The good interelectrodedistance factor can be any appropriate factor, such as 1.1 times thelast known good interelectrode distance. The last known goodinterelectrode distance can be the interelectrode distance measuredimmediately prior to the determination of sheathing.

Further, there is a finite distance that an electrode may travel withinthe heart 80 or vascular system. When past a finite distance, theelectrode will run into an interior wall. Thus, if the PSU 40 tracks anelectrode traveling at a relatively high velocity in a fairly uniformdirection for several samples, then that electrode has likely becomesheathed and is electrically immeasurable. The distance traveled can bedependent upon the known position of the electrode or previous knownposition of the electrode. For example, if it is known that theinstrument was in a confined area, such as near the right ventricleapex, a short distance can be used as a threshold. Otherwise, anyappropriate number of time samples, velocity, or distance can be used todetermined that the electrode has become sheathed.

As discussed above, the most proximal electrode is nearest the sheath inany instrument, such as the ring electrode 110 being proximal on themapping catheter 100 and nearest the sheath 104. Thus, generally, theproximal electrode may be the only electrode to have been sheathed. Whenmarking the electrode as sheathed the entire instrument is marked assheathed. When marked as sheathed, all position information during thetime of marking as sheathed is determined to be invalid. Further, thePSU 40 can provide an indication to a user that the entire instrument issheathed, such as a visual display on the display 58.

PSU Frequency Switching and Blocking

In addition to the various methods and procedures for determining validan invalid data discussed above (e.g. sheath detection, tip-ringcorrection, etc.) others sources of interference or error can bedetected by the PSU 40. The detection or correction of error can bebased on hardware filters, processor determination, or other appropriateprocedures. According to various embodiments, however, frequencies ofcurrent injected into the patient 26 for use other than by the PSU 40may interfere with proper and correct functioning of the electricalfeature used by the PSU 40 to determine a portion of the mappinginstrument or other appropriate instrument.

Determination or bioimpedance and measurement of voltages can be inapplications external to or in addition to the PSU 40. External examplesof bioimpedance include measuring hemodynamic performance, assuringpatient electrode connection, and, other patient specific applications.In particular, the patient 26 may have a pacemaker implanted. If thepatient 26 has an implanted pacemaker and is simultaneously undergoing aprocedure utilizing the PSU 40, interference from the pacemaker mayinterfere with the PSU 40.

The PSU 40 injects a current through the patient 26, measures voltagebetween an electrode pair or pairs, and computes impedance. As discussedabove the PSU 40 can injected current at any appropriate frequency ormultiple frequencies for the different axis patch pairs. The frequenciesare safely tolerated by the patient 26, efficient to detect, and providehigh signal to noise characteristics. If signals are injected into thebody, a system other than the PSU 40, also referred to as anomaloussignals or currents, having may same or similar frequency as used by thePSU 40, the result in the fields being superimposed. If one system isin-band to another, interference can occur with misleading or distortedresults to one or both systems. If interference occurs the anomaloussignal or current, or non-PSU signal, can be an interfering signal orcurrent.

Determination of whether an anomalous interfering signal is present canoccur prior to initiation of position determination with the PSU 40. Todetect if an interfering current or signal is present in the patient 26,the PSU 40 can perform an interference test that includes a signalgeneration and detection system and method. The interference test caninclude, prior to administration or injection of signals into thepatient 26 by the PSU 40, determining whether interfering signals arepresent. If interfering signals are detected, the PSU 40 can then testdetection of the electrodes of the instrument on an alternative, such asan adjacent, frequency. If the alternative frequency is clear, then thesignal generator of the PSU 40 can be switched to the alternativefrequency and the PSU 40 can then be used to determine a position of aposition element, such as the electrode 108, 110 of the mapping catheter100. Accordingly, the PSU 40 can automatically detect whether ananomalous signal is an interfering signal based on in-band detection ofa signal other than that generated by the PSU 40, whether the positioninformation of the mapping catheter 100 is accurate, or otherappropriate methods. The PSU 40 can also automatically switch to afrequency that is not interfered with by the anomalous signal.

A sampling system of the PSU 40 can be invoked to detect if aninterfering signal interprets after a procedure with the PSU 40 begins.The sampling system can perform periodic interference checks to revealif an interfering signal has appeared and switch frequencies in a mannertransparent to the user 22. The sampling system of the PSU 40 canperiodically cease signal generation to enable the detection circuits aperiod and freedom to sense an interfering signal and determine thefrequency of the interfering signal. The periodic interference check canbe manually initiated or automatic. When an interfering signal isdetected a non-interfering frequency or channel can be selected foroperation of the PSU 40. The PSU 40 can then be automatically ormanually switched to a channel that would not be interfered with by theinterfering signal. Having a wide selection of frequencies can allowconcurrent operation.

The sampling system of the PSU 40 can include a system to switchfrequencies for signal generation and detection. In the sampling system,signal generation can used tunable filters such that adjacent frequencyoperation is possible. In other words, once a signal frequency isdetected that would interfere with the signal generation of the PSU 40between the axis patches, the alternative frequency can be selected andgenerated between at least one pair of the axis patches for positiondetermination by the PSU 40. It will also be understood, if aninterfering signal is found or determined to exist the source of thesignal could be blocked or eliminated. For example, an injected currentform a pacemaker could be temporarily eliminated. This can occur inaddition to or alternatively to changing a frequency.

Accordingly, the PSU 40 can be used to determine whether map datadetermined from the position element is valid or not. As discussedabove, prior to initiation of a procedure with the PSU 40 or during aprocedure with the PSU 40, interfering signal sampling can occur. If aninterfering signal is found to be present certain map data can be markedas invalid and discarded or not used to generate the map data points 198or the surface 241. The PSU 40 can also then switch to a non-interferingfrequency, transparently to the user, to continue or begin map datacollection.

Conclusion

The map of the patient 26, or any appropriate subject or feature, can beused as a graphical representation for navigation of an instrument, suchas the lead 120, relative to a physical structure. The map displayed onthe display 58 can be generated without the use of fluoroscopy or otherimaging systems. Therefore, advantages of navigation, such asimage-guided navigation, can be achieved without the need for anexternal imaging device. This can eliminate or reduce exposure of theuser 22 to radiation and decrease procedure times by eliminating orreducing the necessity of requiring the acquisition of image data of thepatient 26.

Further areas of applicability of the present teachings will becomeapparent from the detailed description provided above. It should beunderstood that the detailed description and specific examples, whileindicating various embodiments, are intended for purposes ofillustration only and are not intended to limit the scope of theteachings.

1. A method of determining flow of a material in a volume of a patient,comprising: providing an instrument having a first position element anda flexible body member carrying a second position element operable tomove due to a flow of a fluid in the volume; placing the instrument intothe volume and in contact with the fluid; extending the second positionelement relative to the first position element such that the secondposition element extends a distance from the first position element;determining a position of the second position element relative to thefirst position element due to a movement of the second position elementrelative to the first position element from fluid motion in the volume;and displaying a representation of the determined position of the secondposition element relative to the first position element to illustrate adirection of fluid flow in the volume.
 2. The method of claim 1, whereinplacing the instrument into the volume of the patient includes placingthe instrument into a fluid volume of a cardiovascular system of thepatient.
 3. The method of claim 1, further comprising: providing apassage through a housing of the instrument; placing the first positionelement on an exterior surface of the housing and in contact with thefluid; and providing the flexible body member arranged to be movablypositioned in the passage; wherein extending the second position elementrelative to the first position element includes selectively extending adistal end of the flexible body member beyond the housing so as toextend the second position element a certain distance from the firstposition element.
 4. The method of claim 3, further comprising:determining a plurality of positions of the first and second positionelements in the volume; generating a map based on the determinedplurality of positions; and displaying the map on a display device;determining a location within the patient based on the direction of flowof the material; wherein displaying a graphical representation of thedetermined position of the second element position relevant to the firstelement position includes displaying a graphical representation on thedisplayed map indicative of a direction of movement of the secondposition element relative to the first position element to illustrate adirection of fluid flow in the volume.
 5. The method of claim 3, whereindetermining a position of the second position element relative to thefirst position element includes: evaluating a first electrical propertywith the first position element; determining a position of the firstposition element within the volume based on the evaluated firstelectrical property; evaluating a second electrical property with thesecond position element; and determining a position of the secondposition element relative to the determined position of the firstposition element based on the evaluated second electrical property. 6.The method of claim 5, wherein evaluating the first and secondelectrical properties includes determining an impedance at each of thefirst and second position elements at least by sensing a voltage at eachof the first and second position elements and determining a currentinjected into the volume when the voltage was sensed.
 7. The method ofclaim 5, wherein evaluating the first and second electrical propertiesincludes sensing a respective voltage at the first position element andthe second position element.
 8. The method of claim 5, whereindisplaying a graphical representation of the position of the secondposition element relative to the first position element includes:displaying a graphical representation of the determined position of thefirst position element and the determined position of the secondposition element relative to the first position element; and displayingan additional graphical representation indicative of a direction offluid flow in the volume based on movement of the second positionelement relative to the first position element.
 9. The method of claim8, wherein the additional graphical representation includes an arrowpointing from the determined position of the first position element todetermined position of the second position element to illustrate adirection of fluid flow in the volume.
 10. The method of claim 5,wherein determining a position of the second position element relativeto the first position element includes determining a plurality ofpositions of the second position element relative to the first positionelement; and wherein displaying a graphical representation of thedetermined position of the second position element relative to the firstposition element includes displaying a plurality of graphicalrepresentations indicative of a plurality of directions of fluid flow inthe volume based on a plurality of movements of the second positionelement relative to the first position element.
 11. The method of claim5, further comprising: providing at least one set of axis generationelectrodes on an exterior surface of the volume, the at least one set ofelectrodes arranged to establish an axis via a conductive paththerebetween; and injecting a current into the volume between the atleast one set of electrodes and generating a voltage gradient in thevolume between the at least one set of electrodes; wherein evaluatingthe first and second electrical properties includes sensing voltage atthe first position element and the second position element between theat least one set of electrodes; wherein determining the position of thefirst position element includes determining a position of the sensedvoltage of the first electrical property along the voltage gradientbetween the at least one set of electrodes so as to provide a determinedposition of the first position element; wherein determining the positionof the second position element relative to the position of the firstposition element includes determining a position of the sensed voltageof the second electrical property along the voltage gradient between theat least one set of electrodes so as to provide a determined position ofthe second position element relative to the first position element. 12.The method of claim 5, further comprising: providing three sets of axisgeneration electrodes on an exterior surface of the volume, each set ofelectrodes establishing an axis via a conductive path therebetween, eachaxis of the three sets of electrodes being substantially orthogonal toeach other and intersecting at a common point; and injecting a currentinto the volume between each set of electrodes and generating a voltagegradient in the volume between each set of electrodes; whereinevaluating the first and second electrical properties includes sensingvoltage at the first position element and the second position elementbetween each set of electrodes; wherein determining the position of thefirst position element includes determining a position of the sensedvoltage of the first electrical property along the voltage gradientsbetween each set of electrodes so as to provide a determined threedimensional position of the first position element; wherein determiningthe position of the second position element relative to the position ofthe first position element includes determining a position of the sensedvoltage of the second electrical property along the voltage gradientsbetween each set of electrodes so as to provide a determined threedimensional position of the second position element relative to thefirst position element.
 13. A system for determining a flow of materialin a volume of a patient, comprising: an instrument having a housing anda flexible body member, the housing including proximal and distal endsand an internal passage extending between the proximal and distal ends,the flexible body member arranged to be passed through the housing; afirst position element affixed to an exterior of the housing, wherein aportion of the housing is adapted to be placed in the volume so as toplace the first position element in contact with a fluid in the volumeof the patient; and a second position element affixed to the flexiblebody member, wherein a distal end of the flexible body member isarranged to be selectively extended a certain distance beyond the distalend of the housing so as to place the second position element in contactwith the fluid when the portion of the housing is positioned in thevolume, the extended distal end of the flexible body member operable toflex due to a flow of the fluid in the volume; wherein the firstposition element and the second position element are each arranged tosense an electrical property and provide data for determining a positionof the first position element and a change in position of the secondposition element relative to the first position element, the change inposition of the second position element relative to the first positionelement being indicative of the flow of the fluid in the volume.
 14. Thesystem of claim 13, wherein the first position element and the secondposition element are each arranged to sense a voltage in the volume. 15.The system of claim 14, further comprising: a position sensing unithaving at least one set of axis generation electrodes to inject acurrent into the volume, the at least one set of electrodes adapted tobe positioned on an outer surface of the volume to establish an axis viaa conductive path therebetween, the injected current generating avoltage gradient in the volume between the at least one set ofelectrodes; and a processor coupled to the first and second positionelements, the position sensing unit and a display device, the processorbeing operable to execute instructions to determine the position of thesecond position element relative to the first position element; whereinthe display device is arranged to display a graphical representation ofthe determined position of the second position element relative to thefirst position element to illustrate a direction of fluid flow in thevolume.
 16. The system of claim 15, wherein the processor is furtheroperable to execute instructions to determine a plurality of positionsof the first position element in the volume and generate a map based onthe determined plurality of positions; and wherein the display device isarranged to display the map and to display the graphical representationof the determined position of the second position element relative tothe first position element on the map.
 17. The system of claim 15,wherein the processor is operable to determine a position of the firstposition element based on the sensed voltage along the voltage gradientand a position of the second position element based on the sensedvoltage along the voltage gradient to determine the position of thesecond position element relative to the first position element.
 18. Thesystem of claim 15, wherein the processor is operable to determine animpedance based on the sensed voltage of the first position elementalong the voltage gradient and an impedance based on the second positionelement sensed voltage along the voltage gradient to determine theposition of the second position element relative to the first positionelement.
 19. The system of claim 15, wherein the at least one set ofaxis generation electrodes includes three sets of axis generationelectrodes, each set of the three sets of axis generation electrodesestablishing an axis via a conductive path therebetween, each axis ofthe three sets of electrodes positioned substantially orthogonal to eachother and intersecting at a common point; wherein the processor isoperable to execute instructions to determine a three dimensionalposition of the second position element relative to a three dimensionalposition of the first position element; and wherein the display deviceis arranged to display a graphical representation of the determinedthree dimensional position of the second position element relative tothe first position element to illustrate a direction of fluid flow inthe volume.
 20. The system of claim 15, wherein the display of thegraphical representation of the determined position of the secondposition element relative to the first position element includes: agraphical representation of the determined position of the firstposition element and the determined position of the second positionelement relative to the first position element; and an additionalgraphical representation indicative of a direction of fluid flow in thevolume based on movement of the second position element relative to thefirst position element.
 21. The system of claim 20, wherein theadditional graphical representation includes an arrow pointing from thedetermined position of the first position element to determined positionof the second position element to illustrate a direction of fluid flowin the volume.
 22. The system of claim 14, wherein the first positionelement and the second position element each comprise an electrode. 23.The system of claim 13, wherein the internal passage of the housingfurther comprises an inner diameter and the flexible body member furthercomprises an outer diameter, the outer diameter of the flexible bodymember substantially matching the inner diameter of the passage.
 24. Thesystem of claim 13, wherein the first position element is affixed to thedistal end of the housing and the second position element is affixed tothe distal end of the flexible body member.
 25. A method of determiningflow of a material in a fluid filled volume of a patient, comprising:providing an instrument having a first position element and a flexiblebody member carrying a second position element operable to move due to aflow of a fluid in the volume; placing the instrument into the fluidfilled volume and in contact with the fluid; positioning the secondposition element relative to the first position element such that thesecond position element extends a distance from the first positionelement; determining a first position of the first position elementrelative to a second position of the second position element due to amovement of the second position element relative to the first positionelement because of flow of the fluid in the fluid filled volume; anddetermining a direction of flow of the fluid based on the determinedfirst position relative to the determined second position.